This document describes characteristics of electromagnetic waves and their behavior. It discusses how oscillating charges can generate electromagnetic waves, and how these waves consist of oscillating electric and magnetic fields that propagate perpendicularly. It also covers how electromagnetic waves transfer energy between electric and magnetic fields as they travel at the speed of light.
This document provides an overview of key concepts in wave optics, including:
- Electromagnetic waves and their properties like wavelength and frequency
- Wavefronts and how they are used to describe light propagation
- Huygens' principle which describes how each point on a wavefront acts as a secondary light source
- The laws of reflection and refraction based on Huygens' principle
- How wavefronts behave when interacting with mirrors, lenses, and prisms
- Conditions for coherent and interfering waves
- Young's double slit experiment and the patterns of light and dark fringes it produces
- How thin film interference can produce the colors seen in phenomena like rainbows
1. The document discusses various theories of light propagation including Newton's corpuscular theory, Huygens' wave theory, Maxwell's electromagnetic wave theory, Einstein's quantum theory, and de Broglie's dual theory of light. It explains the key aspects of each theory and whether they can explain various optical phenomena.
2. Topics covered include the nature of light waves, wave fronts, interference and diffraction of light waves, types of interference (constructive and destructive), and Young's double-slit experiment. Key findings of the double-slit experiment are summarized such as the formation of bright and dark interference fringes on the screen.
3. Formulas for path difference, phase difference, resultant amplitude
The document discusses various topics related to wave optics and the physics of light, including:
- The wave nature of light and how it explains phenomena like reflection, refraction, the formation of shadows and spectra.
- Huygens' principle which states that each point on a wavefront is the source of secondary wavelets and the new wavefront is the tangent to these wavelets.
- The laws of reflection which state that the angle of incidence equals the angle of reflection.
- Refraction and how the speed and wavelength of light changes when passing from one medium to another.
- Interference and coherence - the addition of waves to form a resultant wave, and how coherent sources are required
1. Light behaves as a wave and can interfere with itself when it takes multiple paths. Huygens' principle states that each point on a wavefront is a source of secondary wavelets which combine to form the new wavefront.
2. Interference occurs when two waves superimpose, with constructive and destructive interference occurring depending on the path difference between the waves. Young's double slit experiment demonstrated interference and bright and dark fringes formed on the screen.
3. Thin films can produce interference and appear colored due to the path differences between light rays reflecting and refracting within the film, with different colors seen for different path differences satisfying the interference conditions.
This document discusses wave optics and several key concepts:
1. Light exhibits wave characteristics such as interference and diffraction when interacting with objects comparable in size to its wavelength. These phenomena cannot be explained by ray optics alone.
2. Huygens' principle explains how waves propagate and bend around obstacles, known as diffraction. It describes how each point on a wavefront can be seen as a source of secondary wavelets.
3. Young's double slit experiment provides direct evidence of the wave nature of light by producing an interference pattern from two coherent light sources.
4. Other topics covered include single slit diffraction, thin film interference, polarization, and the limits of optical resolution. Wave optics provides explanations for color
Class 12th Physics wave optics ppt part 2 Arpit Meena
This document provides information on various topics related to wave optics, including electromagnetic waves, diffraction, diffraction at a single slit, the theory of diffraction, polarization of light waves, Malus' law, polarization by reflection, and polaroids. Some key points summarized:
- Diffraction is the bending and spreading of light waves around obstacles or through openings, resulting in interference patterns of light and dark fringes. Diffraction occurs due to the superposition of secondary wavelets from the wavefront.
- At a single slit, a central bright fringe and a series of alternating bright and dark fringes are observed at increasing angles from the center. The locations and widths of these fringes can be explained by the theory of
Plane waves have parallel planar wavefronts that propagate indefinitely, while a laser beam has wavefronts that diverge from an initial waist, transitioning from planar to spherical. A laser produces a coherent, monochromatic beam through stimulated emission within an optical cavity. The Gaussian beam equation describes the amplitude, phase, and beam width of a laser beam as it propagates, accounting for its localized amplitude profile and changing wavefront curvature compared to plane waves.
This document discusses the principles and types of diffraction, including Fraunhofer and Fresnel diffraction. It explains diffraction at a single slit and double slit, describing how the diffraction patterns are formed and the conditions for maxima and minima. It also discusses the differences between interference and diffraction. Finally, it discusses diffraction gratings and their uses in spectroscopy.
This document provides an overview of key concepts in wave optics, including:
- Electromagnetic waves and their properties like wavelength and frequency
- Wavefronts and how they are used to describe light propagation
- Huygens' principle which describes how each point on a wavefront acts as a secondary light source
- The laws of reflection and refraction based on Huygens' principle
- How wavefronts behave when interacting with mirrors, lenses, and prisms
- Conditions for coherent and interfering waves
- Young's double slit experiment and the patterns of light and dark fringes it produces
- How thin film interference can produce the colors seen in phenomena like rainbows
1. The document discusses various theories of light propagation including Newton's corpuscular theory, Huygens' wave theory, Maxwell's electromagnetic wave theory, Einstein's quantum theory, and de Broglie's dual theory of light. It explains the key aspects of each theory and whether they can explain various optical phenomena.
2. Topics covered include the nature of light waves, wave fronts, interference and diffraction of light waves, types of interference (constructive and destructive), and Young's double-slit experiment. Key findings of the double-slit experiment are summarized such as the formation of bright and dark interference fringes on the screen.
3. Formulas for path difference, phase difference, resultant amplitude
The document discusses various topics related to wave optics and the physics of light, including:
- The wave nature of light and how it explains phenomena like reflection, refraction, the formation of shadows and spectra.
- Huygens' principle which states that each point on a wavefront is the source of secondary wavelets and the new wavefront is the tangent to these wavelets.
- The laws of reflection which state that the angle of incidence equals the angle of reflection.
- Refraction and how the speed and wavelength of light changes when passing from one medium to another.
- Interference and coherence - the addition of waves to form a resultant wave, and how coherent sources are required
1. Light behaves as a wave and can interfere with itself when it takes multiple paths. Huygens' principle states that each point on a wavefront is a source of secondary wavelets which combine to form the new wavefront.
2. Interference occurs when two waves superimpose, with constructive and destructive interference occurring depending on the path difference between the waves. Young's double slit experiment demonstrated interference and bright and dark fringes formed on the screen.
3. Thin films can produce interference and appear colored due to the path differences between light rays reflecting and refracting within the film, with different colors seen for different path differences satisfying the interference conditions.
This document discusses wave optics and several key concepts:
1. Light exhibits wave characteristics such as interference and diffraction when interacting with objects comparable in size to its wavelength. These phenomena cannot be explained by ray optics alone.
2. Huygens' principle explains how waves propagate and bend around obstacles, known as diffraction. It describes how each point on a wavefront can be seen as a source of secondary wavelets.
3. Young's double slit experiment provides direct evidence of the wave nature of light by producing an interference pattern from two coherent light sources.
4. Other topics covered include single slit diffraction, thin film interference, polarization, and the limits of optical resolution. Wave optics provides explanations for color
Class 12th Physics wave optics ppt part 2 Arpit Meena
This document provides information on various topics related to wave optics, including electromagnetic waves, diffraction, diffraction at a single slit, the theory of diffraction, polarization of light waves, Malus' law, polarization by reflection, and polaroids. Some key points summarized:
- Diffraction is the bending and spreading of light waves around obstacles or through openings, resulting in interference patterns of light and dark fringes. Diffraction occurs due to the superposition of secondary wavelets from the wavefront.
- At a single slit, a central bright fringe and a series of alternating bright and dark fringes are observed at increasing angles from the center. The locations and widths of these fringes can be explained by the theory of
Plane waves have parallel planar wavefronts that propagate indefinitely, while a laser beam has wavefronts that diverge from an initial waist, transitioning from planar to spherical. A laser produces a coherent, monochromatic beam through stimulated emission within an optical cavity. The Gaussian beam equation describes the amplitude, phase, and beam width of a laser beam as it propagates, accounting for its localized amplitude profile and changing wavefront curvature compared to plane waves.
This document discusses the principles and types of diffraction, including Fraunhofer and Fresnel diffraction. It explains diffraction at a single slit and double slit, describing how the diffraction patterns are formed and the conditions for maxima and minima. It also discusses the differences between interference and diffraction. Finally, it discusses diffraction gratings and their uses in spectroscopy.
This document provides an overview of key concepts in ray optics, including:
1. Refraction is defined as the change in direction and speed of light when passing from one medium to another. Snell's law describes the relationship between angles of incidence and refraction.
2. Total internal reflection occurs when light passes from an optically dense to a rare medium at an angle greater than the critical angle, causing the light to reflect back into the dense medium.
3. Spherical lenses can be either convex or concave. The lens maker's formula and thin lens equation describe the imaging properties and magnification of thin lenses based on the focal length and object and image distances.
1. Light has both wave and particle properties, though historically there were separate theories proposing one or the other.
2. Thomas Young's double slit experiment provided early evidence of light's wave nature by producing interference patterns. Other experiments like thin film interference and diffraction around obstacles further supported this.
3. Albert Einstein explained the photoelectric effect by proposing light also behaves as discrete packets of energy called photons, providing evidence of its particle nature.
This document discusses several phenomena that demonstrate the wave-like properties of light, including diffraction, interference, polarization, and the photoelectric effect. It describes key experiments such as Young's double slit experiment and explains concepts such as Huygens' principle, Brewster's angle, and how diffraction patterns are formed. It also defines important terms for waves like wavelength, frequency, and the relationship between them given by the speed of light.
This document discusses the phenomenon of diffraction - how light bends or spreads when encountering an obstacle or opening. It provides details on diffraction patterns created by single slits, edges, and gratings. Key points covered include the characteristics of diffraction patterns such as bright and dark bands, as well as the differences between Fresnel and Fraunhofer diffraction based on the distances between the light source, obstacle, and viewing screen. Equations for determining the positions of maxima and minima in diffraction patterns are also presented.
The document describes an experiment using a diffraction grating spectrometer to measure emission spectra of elements and identify unknown elements. Sodium light is used to calibrate the spectrometer by measuring the angles of the first and second order spectra and calculating the grating spacing. Then an unknown light is analyzed by measuring spectral line angles and wavelengths, which are compared to reference tables to identify the element.
Ch 27 interference & wave nature of light onlineScott Thomas
The document discusses key concepts related to the wave nature of light and interference and diffraction phenomena:
1) Interference occurs when two light waves pass through a point and their electric fields combine according to the principle of superposition, resulting in constructive or destructive interference depending on whether the waves are in or out of phase.
2) Young's double-slit experiment demonstrates interference, producing bright and dark fringes on a screen from the constructive and destructive interference of light passing through two slits.
3) Thin-film interference results from the multiple reflections within a thin film, leading to either constructive or destructive interference depending on the path length differences and refractive indices of the materials.
This document summarizes key concepts in wave optics, including:
1. Diffraction occurs when light bends around obstacles and into regions of geometric shadows. Diffraction patterns from a single slit include a central maximum surrounded by alternating dark and bright fringes whose angles follow mathematical formulas.
2. The theory of diffraction is based on the principle of interference of secondary wavelets emerging from different parts of a wavefront.
3. Polarization of light waves occurs as the electric field oscillates perpendicular to the direction of propagation, and polarizers and analyzers can be used to study polarized light according to Malus' Law.
The document discusses the principles of diffraction gratings and how they can be used to calculate various properties of light. Specifically, it explains the diffraction grating equation, provides examples of how to use it to determine the wavelength of light and angle of diffraction for different grating spacings and orders. It also describes how a grating's line spacing can be used to calculate the slit spacing and discusses the angular spread of a spectrum produced from a grating.
1. The document discusses various wave optics phenomena including interference, diffraction, and thin film interference.
2. Key concepts covered include the Michelson interferometer, conditions for constructive and destructive interference, single and double slit diffraction experiments, and how thin films can produce interference patterns based on their thickness.
3. Examples are provided to demonstrate how concepts like wavelength can be measured using interference patterns from double slit experiments.
1) Fresnel's theory of diffraction explains that diffraction occurs due to the interference of secondary wavelets produced by unobstructed portions of the wavefront.
2) When considering the diffraction pattern at a point P, Fresnel divided the wavefront into concentric half-period zones centered on the point's pole O. The contribution of each zone to the intensity at P depends on the zone's area and distance from P.
3) For a large number of zones, the total intensity at P is approximately one fourth of that due to the first zone alone, explaining the dimming of light in diffraction patterns.
This document discusses the principles and phenomena of diffraction. It begins by defining diffraction as the deviation of light from rectilinear propagation that occurs when a portion of a wavefront is obstructed. The Huygens-Fresnel principle is introduced, which states that every point on a wavefront acts as a secondary source of spherical wavelets. Diffraction patterns can be classified as either Fraunhofer or Fresnel diffraction depending on the separation between the aperture and viewing screen. Examples of diffraction from single slits, circular apertures, and double slits are analyzed. Rayleigh's criterion for resolving power with rectangular apertures is also described.
1) Diffraction refers to the spreading or bending of waves around edges, which results in a characteristic fringe pattern from a single slit consisting of alternating bright and dark fringes that fade from the center.
2) Interference patterns from thin films and multiple slits can be explained by the optical path difference between light waves reflecting or diffracting from different points, with constructive and destructive interference occurring at specific path differences.
3) A diffraction grating splits light into multiple beams at specific angles determined by the grating spacing and wavelength, allowing spectrometers to measure light wavelengths.
1. Diffraction refers to the bending of light around obstacles or through openings, and results in interference patterns.
2. There are two main types of diffraction: Fresnel diffraction occurs when light passes near an obstacle, while Fraunhofer diffraction occurs when light passes through or around objects and the observation is made far from the obstacle.
3. Diffraction gratings consist of many parallel slits and cause light to diffract into several beams. The angles and intensities of these beams can be determined through analysis of interference from the multiple slits.
When two light waves pass through the same point in space simultaneously, interference occurs. Constructive interference happens when the waves are in phase and add to produce a larger wave, while destructive interference occurs when they are out of phase and cancel each other out. The intensity of the resulting interference pattern depends on the phase difference between the waves. In a double slit experiment, the phase difference and resulting interference is determined by the path length difference between waves passing through each slit.
Radiometry is the science of measuring radiation, including separate wavelengths across the electromagnetic spectrum. Photometry specifically measures light visible to the human eye.
Key radiometric quantities include radiant flux (watts), irradiance (watts/m2), and radiance (watts/m2/sr). Key photometric quantities are luminous flux (lumens), illuminance (lux), and luminance (candelas/m2). These radiometric and photometric quantities are related through the CIE luminous efficiency curve.
Blackbody radiation follows Planck's law, Stefan-Boltzmann law, and Wien's displacement law, describing the spectral distribution and total power of electromagnetic radiation emitted by a
The document discusses the principles and applications of diffraction. It defines diffraction as how waves spread out when passing through an aperture. The amount of diffraction depends on the ratio of the wavelength to the aperture width. A single slit produces a diffraction pattern of bright and dark fringes. Multiple slits produce an interference pattern as each slit acts as a point source. Diffraction gratings can be used to accurately measure wavelengths and produce spectra by separating wavelengths. Applications include measuring unknown wavelengths, identifying materials through their spectra, and determining the composition of stars and nebulae.
This document discusses several topics related to diffraction:
- Diffraction occurs when light encounters multiple beams, such as through diffraction gratings with many slits or apertures.
- Diffraction gratings display interference patterns that follow the grating equation and can be used for spectroscopy and laser tuning.
- Fabry-Perot interferometers create multiple beam interference between partially reflecting mirrors, producing a series of evenly spaced transmission peaks used for linewidth measurement and laser narrowing.
- Diffraction at an aperture, such as a single slit, results in qualitative effects on the diffraction pattern that change with propagation distance.
Light waves superimpose each other and the redistribution of energy due to this can be observed in terms of well defined patterns of maxima and minima. Wherein, maxima refers to more energy and minima refers to less energy. Diffraction can also be called as interference in secondary wavelets.
This article speaks about the optical phenomenon of diffraction. The terms related to it. This article explains the principle of diffraction and provides a comprehensive understanding for the students of optics.
1. Dr. Vishal Jain will be giving a lecture series on engineering physics covering topics such as wave optics and interference.
2. The document discusses the principles of wave optics including interference, diffraction, polarization and introduces the Michelson interferometer.
3. Examples of how the Michelson interferometer can be used to measure wavelength and the difference between two nearby wavelengths are shown through problems and solutions.
This document discusses electromagnetic waves and their properties. It covers topics such as waves in one dimension, electromagnetic waves in vacuum, electromagnetic waves in matter, absorption and dispersion, and guided waves. Key points include that electromagnetic waves satisfy Maxwell's equations and the wave equation in vacuum and matter. They can be reflected, transmitted, and absorbed at boundaries. Guided waves can propagate down wave guides and transmission lines.
The document discusses photovoltaic devices and solar cells. It begins by introducing photovoltaic devices and how they convert solar radiation into electrical energy. It then discusses the solar energy spectrum and how sunlight intensity is affected by atmospheric absorption and scattering. The principles of photovoltaic devices are explained, including how photons are absorbed to generate charge carriers, and the operation of pn junction solar cells. Applications ranging from small electronics to large solar power plants are mentioned. Key factors that influence solar cell efficiency such as materials properties, surface recombination, and wavelength absorption are analyzed.
This document provides an overview of key concepts in ray optics, including:
1. Refraction is defined as the change in direction and speed of light when passing from one medium to another. Snell's law describes the relationship between angles of incidence and refraction.
2. Total internal reflection occurs when light passes from an optically dense to a rare medium at an angle greater than the critical angle, causing the light to reflect back into the dense medium.
3. Spherical lenses can be either convex or concave. The lens maker's formula and thin lens equation describe the imaging properties and magnification of thin lenses based on the focal length and object and image distances.
1. Light has both wave and particle properties, though historically there were separate theories proposing one or the other.
2. Thomas Young's double slit experiment provided early evidence of light's wave nature by producing interference patterns. Other experiments like thin film interference and diffraction around obstacles further supported this.
3. Albert Einstein explained the photoelectric effect by proposing light also behaves as discrete packets of energy called photons, providing evidence of its particle nature.
This document discusses several phenomena that demonstrate the wave-like properties of light, including diffraction, interference, polarization, and the photoelectric effect. It describes key experiments such as Young's double slit experiment and explains concepts such as Huygens' principle, Brewster's angle, and how diffraction patterns are formed. It also defines important terms for waves like wavelength, frequency, and the relationship between them given by the speed of light.
This document discusses the phenomenon of diffraction - how light bends or spreads when encountering an obstacle or opening. It provides details on diffraction patterns created by single slits, edges, and gratings. Key points covered include the characteristics of diffraction patterns such as bright and dark bands, as well as the differences between Fresnel and Fraunhofer diffraction based on the distances between the light source, obstacle, and viewing screen. Equations for determining the positions of maxima and minima in diffraction patterns are also presented.
The document describes an experiment using a diffraction grating spectrometer to measure emission spectra of elements and identify unknown elements. Sodium light is used to calibrate the spectrometer by measuring the angles of the first and second order spectra and calculating the grating spacing. Then an unknown light is analyzed by measuring spectral line angles and wavelengths, which are compared to reference tables to identify the element.
Ch 27 interference & wave nature of light onlineScott Thomas
The document discusses key concepts related to the wave nature of light and interference and diffraction phenomena:
1) Interference occurs when two light waves pass through a point and their electric fields combine according to the principle of superposition, resulting in constructive or destructive interference depending on whether the waves are in or out of phase.
2) Young's double-slit experiment demonstrates interference, producing bright and dark fringes on a screen from the constructive and destructive interference of light passing through two slits.
3) Thin-film interference results from the multiple reflections within a thin film, leading to either constructive or destructive interference depending on the path length differences and refractive indices of the materials.
This document summarizes key concepts in wave optics, including:
1. Diffraction occurs when light bends around obstacles and into regions of geometric shadows. Diffraction patterns from a single slit include a central maximum surrounded by alternating dark and bright fringes whose angles follow mathematical formulas.
2. The theory of diffraction is based on the principle of interference of secondary wavelets emerging from different parts of a wavefront.
3. Polarization of light waves occurs as the electric field oscillates perpendicular to the direction of propagation, and polarizers and analyzers can be used to study polarized light according to Malus' Law.
The document discusses the principles of diffraction gratings and how they can be used to calculate various properties of light. Specifically, it explains the diffraction grating equation, provides examples of how to use it to determine the wavelength of light and angle of diffraction for different grating spacings and orders. It also describes how a grating's line spacing can be used to calculate the slit spacing and discusses the angular spread of a spectrum produced from a grating.
1. The document discusses various wave optics phenomena including interference, diffraction, and thin film interference.
2. Key concepts covered include the Michelson interferometer, conditions for constructive and destructive interference, single and double slit diffraction experiments, and how thin films can produce interference patterns based on their thickness.
3. Examples are provided to demonstrate how concepts like wavelength can be measured using interference patterns from double slit experiments.
1) Fresnel's theory of diffraction explains that diffraction occurs due to the interference of secondary wavelets produced by unobstructed portions of the wavefront.
2) When considering the diffraction pattern at a point P, Fresnel divided the wavefront into concentric half-period zones centered on the point's pole O. The contribution of each zone to the intensity at P depends on the zone's area and distance from P.
3) For a large number of zones, the total intensity at P is approximately one fourth of that due to the first zone alone, explaining the dimming of light in diffraction patterns.
This document discusses the principles and phenomena of diffraction. It begins by defining diffraction as the deviation of light from rectilinear propagation that occurs when a portion of a wavefront is obstructed. The Huygens-Fresnel principle is introduced, which states that every point on a wavefront acts as a secondary source of spherical wavelets. Diffraction patterns can be classified as either Fraunhofer or Fresnel diffraction depending on the separation between the aperture and viewing screen. Examples of diffraction from single slits, circular apertures, and double slits are analyzed. Rayleigh's criterion for resolving power with rectangular apertures is also described.
1) Diffraction refers to the spreading or bending of waves around edges, which results in a characteristic fringe pattern from a single slit consisting of alternating bright and dark fringes that fade from the center.
2) Interference patterns from thin films and multiple slits can be explained by the optical path difference between light waves reflecting or diffracting from different points, with constructive and destructive interference occurring at specific path differences.
3) A diffraction grating splits light into multiple beams at specific angles determined by the grating spacing and wavelength, allowing spectrometers to measure light wavelengths.
1. Diffraction refers to the bending of light around obstacles or through openings, and results in interference patterns.
2. There are two main types of diffraction: Fresnel diffraction occurs when light passes near an obstacle, while Fraunhofer diffraction occurs when light passes through or around objects and the observation is made far from the obstacle.
3. Diffraction gratings consist of many parallel slits and cause light to diffract into several beams. The angles and intensities of these beams can be determined through analysis of interference from the multiple slits.
When two light waves pass through the same point in space simultaneously, interference occurs. Constructive interference happens when the waves are in phase and add to produce a larger wave, while destructive interference occurs when they are out of phase and cancel each other out. The intensity of the resulting interference pattern depends on the phase difference between the waves. In a double slit experiment, the phase difference and resulting interference is determined by the path length difference between waves passing through each slit.
Radiometry is the science of measuring radiation, including separate wavelengths across the electromagnetic spectrum. Photometry specifically measures light visible to the human eye.
Key radiometric quantities include radiant flux (watts), irradiance (watts/m2), and radiance (watts/m2/sr). Key photometric quantities are luminous flux (lumens), illuminance (lux), and luminance (candelas/m2). These radiometric and photometric quantities are related through the CIE luminous efficiency curve.
Blackbody radiation follows Planck's law, Stefan-Boltzmann law, and Wien's displacement law, describing the spectral distribution and total power of electromagnetic radiation emitted by a
The document discusses the principles and applications of diffraction. It defines diffraction as how waves spread out when passing through an aperture. The amount of diffraction depends on the ratio of the wavelength to the aperture width. A single slit produces a diffraction pattern of bright and dark fringes. Multiple slits produce an interference pattern as each slit acts as a point source. Diffraction gratings can be used to accurately measure wavelengths and produce spectra by separating wavelengths. Applications include measuring unknown wavelengths, identifying materials through their spectra, and determining the composition of stars and nebulae.
This document discusses several topics related to diffraction:
- Diffraction occurs when light encounters multiple beams, such as through diffraction gratings with many slits or apertures.
- Diffraction gratings display interference patterns that follow the grating equation and can be used for spectroscopy and laser tuning.
- Fabry-Perot interferometers create multiple beam interference between partially reflecting mirrors, producing a series of evenly spaced transmission peaks used for linewidth measurement and laser narrowing.
- Diffraction at an aperture, such as a single slit, results in qualitative effects on the diffraction pattern that change with propagation distance.
Light waves superimpose each other and the redistribution of energy due to this can be observed in terms of well defined patterns of maxima and minima. Wherein, maxima refers to more energy and minima refers to less energy. Diffraction can also be called as interference in secondary wavelets.
This article speaks about the optical phenomenon of diffraction. The terms related to it. This article explains the principle of diffraction and provides a comprehensive understanding for the students of optics.
1. Dr. Vishal Jain will be giving a lecture series on engineering physics covering topics such as wave optics and interference.
2. The document discusses the principles of wave optics including interference, diffraction, polarization and introduces the Michelson interferometer.
3. Examples of how the Michelson interferometer can be used to measure wavelength and the difference between two nearby wavelengths are shown through problems and solutions.
This document discusses electromagnetic waves and their properties. It covers topics such as waves in one dimension, electromagnetic waves in vacuum, electromagnetic waves in matter, absorption and dispersion, and guided waves. Key points include that electromagnetic waves satisfy Maxwell's equations and the wave equation in vacuum and matter. They can be reflected, transmitted, and absorbed at boundaries. Guided waves can propagate down wave guides and transmission lines.
The document discusses photovoltaic devices and solar cells. It begins by introducing photovoltaic devices and how they convert solar radiation into electrical energy. It then discusses the solar energy spectrum and how sunlight intensity is affected by atmospheric absorption and scattering. The principles of photovoltaic devices are explained, including how photons are absorbed to generate charge carriers, and the operation of pn junction solar cells. Applications ranging from small electronics to large solar power plants are mentioned. Key factors that influence solar cell efficiency such as materials properties, surface recombination, and wavelength absorption are analyzed.
Light has several properties that make it useful for information processing and optical communication systems. It can be transmitted without interference from electrical signals or other light beams crossing its path. Optical signals also allow high parallelism and bandwidth exceeding 1013 bits per second. Radiation sources can be classified by their flux output and spectrum. Light behaves as an electromagnetic wave that propagates through space as oscillating electric and magnetic fields. In a material medium, the light's phase velocity decreases and is characterized by the medium's refractive index. Crystalline materials exhibit anisotropic refractive indices depending on the propagation and polarization directions.
The document discusses various uses of radio waves beyond radio broadcasting, including television which uses amplitude and frequency modulation to transmit audio and video signals, infrared which can transmit small data packets but requires line of sight, and satellite navigation which uses signals from multiple satellites to determine location. It also covers Wi-Fi which transmits data wirelessly using radio signals, mobile networks which transmit voice data via microwave radiation, and radar which detects objects by transmitting radio waves and receiving signals bounced back.
1. Waves transfer energy from one place to another through a medium without transferring matter. They are produced by a vibrating or oscillating source and can be transverse or longitudinal.
2. Key wave properties include amplitude, wavelength, period, frequency, and speed. Amplitude is the maximum displacement from equilibrium, wavelength is the distance between peaks, period is time for one cycle, frequency is cycles per second, and speed depends on wavelength and frequency.
3. Waves can be characterized by displacement-time graphs showing oscillation over time or displacement-distance graphs showing the pattern of compression and rarefaction as the wave propagates through a medium.
Radio waves are a type of electromagnetic radiation that have long wavelengths compared to other waves like infrared and gamma rays. They transmit information such as music, pictures, and conversation through modulation of their amplitude or frequency. Radio waves are used for technologies like radio, television, wireless networks, GPS, and mobile phones by encoding signals onto continuous sine waves that transmit from antennas.
Radio waves are electromagnetic waves that can range in length from millimeters to over 100,000 km, making them one of the largest types of waves. They are used to transmit signals for radio, television, mobile phones, and other technologies. Radio waves are transmitted through antennas and received by antennas, where a tuner selects the desired frequency. Mobile phones also emit low levels of radio frequency radiation when in use. Television has transitioned from using antennas to receive radio wave signals to digital transmission of signals through networks.
This presentation gives an information about: photoelasticity, covering syllabus of Unit-3, of Experimental stress analysis subject for BE course under Visvesvaraya Technological University (VTU), Belgaum.
Polarization of Light and its Application (healthkura.com)Bikash Sapkota
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polarization of light & its application.
PRESENTATION LAYOUT
Concept of Polarization
Types of Polarization
Methods of achieving Polarization
Applications of Polarization
POLARIZATION
Transforming unpolarized light into polarized light
Restriction of electric field vector E in a particular plane so that vibration occurs in a single plane
Characteristic of transverse wave
Longitudinal waves can’t be polarized; direction of their oscillation is along the direction of propagation.............
For Further Reading
•Optics by Tunnacliffe
•Optics and Refraction by A.K. Khurana
•Principle of Physics, Ayam Publication
•Internet
Waves can be transverse or longitudinal. Transverse waves have vibrations perpendicular to the direction of travel, like water waves. Longitudinal waves have vibrations parallel to travel, like sound waves. The characteristics of all waves include amplitude, wavelength, frequency, period, and speed. Wavelength is the distance between two peaks, frequency is the number of waves passing a point per second, and speed equals wavelength times frequency.
The document is a presentation about electromagnetic waves. It contains the following key points:
1. Electromagnetic waves include radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. They are classified based on wavelength and frequency.
2. All electromagnetic waves are transverse waves that travel at the speed of light and can be reflected, refracted, emitted or absorbed.
3. Different types of electromagnetic waves have various applications like radio for communication, infrared for night vision, visible light for sight, ultraviolet for sterilization, X-rays for medical imaging and gamma rays for cancer treatment.
4. Students are instructed to read the presentation, take an
This document discusses radio waves and their uses. It defines radio waves as a type of electromagnetic radiation with wavelengths longer than infrared light that can transmit frequencies over long or short distances. Radio waves are used for technologies like mobile phones, Bluetooth, wireless networks, radio, television and more. The document describes how radio antennas receive signals and how radio waves are used in mobile devices and television transmission. It also discusses radio wave transmission methods and the importance of radio waves in modern society.
Interference occurs when two or more waves pass through the same space and can be constructive or destructive. Constructive interference occurs when waves are in phase and amplitudes add, while destructive interference occurs when waves are out of phase and amplitudes cancel. Light interference can be observed using Young's double slit experiment, which uses a coherent monochromatic light source like a laser. The experiment produces bright and dark interference fringes that can be used to determine wavelength according to the equation dsinθ=mλ. Diffraction gratings produce sharper interference patterns than double slits and allow measuring the wavelengths of light in a spectrum.
1. Electromagnetic radiation consists of oscillating electric and magnetic fields perpendicular to each other that are classified according to frequency and wavelength from radio to gamma rays.
2. When electrons in atoms gain and lose energy, electromagnetic energy is released as pulses. Interference occurs when waves combine constructively or destructively. Reflection, refraction, and absorption change the direction and propagation of electromagnetic waves when they encounter different media.
3. Scattering alters the direction of some electromagnetic rays as they pass through non-homogeneous matter, reducing penetration depth. Key wave properties like wavelength, frequency, reflection, refraction, interference and absorption are important for understanding electromagnetic radiation.
Optical interferometry uses light interference to provide extremely precise measurements. When two light waves are combined, they can produce interference fringes of light and dark bands that contain information about the optical path differences between the waves. Recent advances in lasers, fiber optics, and digital processing have expanded applications of optical interferometry from measuring molecular sizes to diameters of stars.
The document is a physics investigatory project submitted by Jiya Saini of Class 12 A to their physics teacher Rakhi. It discusses the topic of diffraction of light. The project includes an acknowledgement, certificate, preface, and sections on what is diffraction, the history of diffraction, when and how it occurs, types of diffraction including single and double slit diffraction, examples and applications, and an experimental analysis of single slit diffraction.
1. Physical Optics deals with the wave nature of light, specifically electromagnetic waves described by Maxwell's equations, whereas Geometrical Optics deals with the particle nature of light.
2. Maxwell established that light is an electromagnetic wave that propagates through space at a constant speed. Hertz later produced electromagnetic waves experimentally.
3. Interference and diffraction of light can be explained using Huygens' principle that each point on a wavefront acts as a secondary source emitting spherical wavelets. This allows prediction of phenomena like interference patterns, reflection and refraction of light.
The document summarizes key concepts about radio wave propagation including:
- Radio waves are transmitted from antennas and can propagate through line of sight transmission, reflection off the ionosphere (skywaves), or along the ground (groundwaves).
- The ionosphere, ionized by solar radiation, is made up of layers (D, E, F1, F2) that refract radio waves to different extents based on frequency and solar activity.
- Solar activity and sunspots influence ionization and radio propagation, with higher activity providing better long-distance propagation via skywaves.
When waves encounter obstacles like slits, they diffract or bend around the edges. Diffraction can be explained by Huygens' principle, which says each point on a wavefront acts as a new source. For a single slit, the new wavefront shape is determined by combining spherical wavelets from points across the slit. There are two types of diffraction: Fresnel, where distances are finite, and Fraunhofer, where incident waves are plane waves. X-ray diffraction uses wavelengths comparable to atomic sizes to determine crystal and molecular structures.
Waves can be categorized as mechanical or electromagnetic. Mechanical waves require a medium to travel through, while electromagnetic waves do not. Waves can also be transverse or longitudinal depending on the direction of particle oscillation relative to wave propagation. Important wave properties include amplitude, wavelength, frequency, and speed. Reflection, refraction, diffraction, interference, and polarization are key wave phenomena. Reflection follows the laws of reflection, while refraction follows Snell's law. Diffraction and interference result in constructive and destructive patterns. Polarization occurs when waves vibrate in a single plane. Waves have many applications including ultrasound imaging, fiber optics, and 3D displays.
Wave motion transfers energy from one place to another. There are two main types of waves: transverse waves where particles oscillate perpendicular to the wave direction, and longitudinal waves where particles oscillate parallel to the wave direction. Key wave properties include amplitude, wavelength, frequency, and phase. Waves can undergo various interactions including reflection, refraction, diffraction, interference, and superposition. Interference of waves leads to constructive and destructive interference patterns. Standing waves occur due to interference of waves traveling in opposite directions.
Interference of light refers to the redistribution of light energy due to superposition of two light waves. This superposition leads to a pattern of alternate dark and bright fringes. These dark and bright fringes are called as minima and maxima respectively.
This document discusses various topics related to wave propagation and radio frequency communications. It begins by explaining Maxwell's equations and how electric and magnetic fields are produced. It then describes different modes of radio wave propagation including ground waves, space waves, sky waves, and tropospheric scattering. The document discusses the layers of the atmosphere and how the ionosphere refracts radio waves to allow long distance sky wave propagation. It also explains how solar activity and the sun's 11-year cycle affects the ionosphere and usable radio frequencies. Finally, it provides definitions for various terms related to radio wave propagation and communications.
The document provides information on wave propagation including:
1) It discusses Maxwell's equations and how electric and magnetic fields relate to wave propagation.
2) It describes different modes of propagation including ground waves, space waves, and sky waves. Sky waves involve reflection between the ionosphere and ground to allow long distance transmission.
3) Factors like solar activity and sunspots impact the ionosphere and affect the highest usable frequency for sky wave propagation at different times.
Paras Sundriyal presented on the topic of interference to Mrs. Ramna Tripathi. They discussed key concepts of interference including coherent sources, conditions for interference, and types of interference like constructive and destructive. Specific experiments were covered like Young's double slit experiment, fringe width, displacement of fringes, Stokes treatment, and Newton's rings experiment using a plano-convex lens and glass plate to form interference patterns. The presentation aimed to provide a clearer understanding of interference beyond the typical syllabus.
Light can be defined as energy that the human eye can see. There are three broad subfields of optics: geometrical optics which studies light as rays, physical optics which studies light as waves, and quantum optics which studies light as particles. Geometrical optics includes the laws of reflection and refraction. Physical optics demonstrates that light exhibits wave properties through interference and diffraction. Quantum optics examines light at the quantum scale. Polarization and dispersion are also properties of light discussed in the document. Visual field loss in glaucoma can be detected earlier using blue light stimuli on a yellow background due to the eye's sensitivity to different wavelengths.
Radio waves can propagate through free space or be guided by surfaces like the ground or the ionosphere. The key layers of the ionosphere that influence radio propagation are the D, E, and F layers. The F layer, consisting of the F1 and F2 sublayers, is the most important for long-distance radio communications as it remains partially ionized at night. Radio signals can be reflected or refracted by the ionized layers of the ionosphere, allowing skywave propagation over long distances beyond the horizon.
Wave interference occurs when two waves interact within the same medium. When the crests of two waves meet, it causes constructive interference and increased amplitude. When the crest of one wave meets the trough of the other, it causes destructive interference and very calm water with no amplitude. Nodal lines form patterns that mark regions of constructive and destructive interference. The distance between nodal lines is related to the wavelength of the interfering waves. Understanding wave interference is important for more complex examples like the double slit experiment.
This document discusses several aspects of diffraction and polarization of light. It begins by introducing diffraction and how it occurs when light encounters an obstacle or aperture. It then discusses single-slit diffraction and how a slit wider than the wavelength of light produces interference patterns downstream. Next, it explains how to calculate the angle for destructive interference using the path difference between light from different points across the slit. It also discusses diffraction from circular apertures and the Airy disk pattern. Finally, it defines polarization as the orientation of oscillations in transverse waves and discusses polarized and unpolarized light.
The document discusses reflection and transmission of mechanical waves at discontinuities in materials. It explains that waves can be reflected, transmitted, or absorbed depending on whether the wave's frequency matches the object's natural vibration frequencies. Reflection occurs if vibrations are not passed through the material, while transmission occurs if vibrations pass through. The document then applies these concepts to analyze reflection and transmission of pressure waves in arteries at locations where properties change, like narrowing, widening, or bifurcations into branches. Mathematical formulas are presented to calculate reflection and transmission coefficients at such discontinuities.
Radio waves are electromagnetic waves that propagate through free space as transverse electromagnetic waves, with the electric field, magnetic field, and direction of propagation being mutually perpendicular. When emitted by an antenna, radio waves travel through space and are affected by objects they encounter, with the signal strength decreasing with distance from the transmitter due to the inverse square law. Radio waves can be reflected, refracted, diffracted, and focused similar to light waves.
Here is a semi-log plot of the data with an exponential trendline:
The equation of the trendline is:
y = 12456e-0.4693x
Taking the natural log of both sides:
ln(y) = ln(12456) - 0.4693x
The slope is -0.4693
Using the equation:
t1/2 = 0.693/λ
λ = 0.4693
t1/2 = 0.693/0.4693 = 1.5
Therefore, the half-life of the isotope is 1.5 intervals, or 1.5 x 30 s = 45 seconds.
This document discusses the photoelectric effect and how it relates to classical and quantum theories of light. It begins by describing early observations of the photoelectric effect and how it works. It then outlines several predictions of classical theory that did not match experimental observations, such as intensity of light not affecting electron kinetic energy. Einstein's explanation using a quantum theory approach is then presented, introducing the concept of photons. Several actual observations from experiments are then matched to explanations using quantum theory. The document concludes by discussing de Broglie's hypothesis of matter waves and how particles can behave as waves.
This document discusses electromagnetic induction and how it is used to generate alternating current (AC) in generators. It explains that rotating coils within a magnetic field generate an electromotive force (EMF) that produces a current. The current flows back and forth as the coils rotate, making it an alternating current. It describes the key components of a basic AC generator, including the coil, slip rings, and brushes. The output is a sinusoidal waveform where the current is maximum when the coil's motion cuts the most magnetic field lines per unit time. It also discusses how transformers are used to change AC voltages by using the principle of electromagnetic induction.
There are three main forms of heat transfer: conduction, convection, and radiation. Conduction involves the transfer of kinetic energy between particles in direct contact. Convection involves the transfer of heat by the movement of fluids like gases and liquids. Radiation involves the transfer of energy through electromagnetic waves and does not require a medium. Increased concentrations of greenhouse gases like carbon dioxide and methane in the atmosphere have intensified the natural greenhouse effect, contributing to global warming by trapping more heat in the lower atmosphere. The impacts of climate change include rising temperatures, changes to climate and weather patterns, rising sea levels, and disruption of natural ecosystems.
The document discusses various renewable and non-renewable energy sources. It provides information on how different energy sources work, including fossil fuels like coal, oil and gas, as well as renewable sources like solar, wind, hydroelectric, geothermal, and nuclear. It discusses the basic processes of energy conversion, emissions, costs and environmental impacts of each energy source. Sankey diagrams are also introduced to illustrate energy transfers from different fuel sources.
The energy falling on a 1 m^2 surface on Earth in a year is:
Lsun x π x 1 x (1 year) = 3.90x1026 W x π x 1 x (3600 s/hr x 24 hr/day x 365.25 day/year) = 1.36x1017 J
Where Lsun is the luminosity of the Sun (3.90x1026 W) and 1 year is converted to seconds.
The Big Bang model describes the origin and evolution of our universe. It postulates that approximately 13.8 billion years ago, the entire observable universe was only a few millimeters in size and extremely hot and dense. The universe has been expanding and cooling ever since. Evidence for the Big Bang includes the expansion of the universe, the cosmic microwave background radiation, and the relative abundance of light elements like hydrogen and helium.
Ernst Rutherford conducted an experiment where he fired alpha particles at a thin gold foil. Most passed straight through but some were scattered back at wide angles. This was unexpected and led Rutherford to propose that atoms have a small, dense nucleus containing positive charge. Later, models showed this could explain the scattering if alpha particles passed close enough to the nucleus to be strongly repelled by its positive charge. This nuclear model revolutionized understanding of atomic structure.
- Nuclear fission involves splitting large nuclei like uranium, releasing energy. Fusion joins light nuclei like hydrogen, also releasing energy.
- Fission is used in nuclear power plants and bombs. Fusion powers stars and could be an energy source on Earth if containment and high temperature issues are solved.
- The binding energy curve shows that mid-sized nuclei are most stable, and that fission and fusion involving less stable nuclei release energy.
7.1 Atomic, nuclear and particle physicsPaula Mills
This document discusses atomic, nuclear and particle physics concepts including:
- Atomic energy levels and line spectra which provide evidence that electrons can only have certain discrete energy values within an atom.
- The Bohr model of the atom which assumed quantized electron energy levels and explained hydrogen atom spectra.
- Nuclear structure including mass number, nucleons, atomic number, isotopes, and interactions within the nucleus.
- Three types of nuclear radiation - alpha, beta, and gamma rays - and how they differ in their ionizing properties and penetration abilities due to their mass and charge.
- Nuclear stability and how heavier nuclei require more neutrons to counter the repulsive force between protons.
- Two
This document defines capacitance as the charge per unit voltage that a device can maintain. It describes a capacitor as a device that can store charge, consisting of two parallel plates separated by a medium like air, vacuum, or dielectric. It provides the equations for capacitance and discusses how capacitors can be arranged in series or parallel circuits. It also describes how capacitors can be used to store energy and discusses dielectrics and their effect on capacitance. Examples are given of calculating charge, capacitance, and capacitor arrangements in circuits.
This document discusses electromagnetic induction and Faraday's law of induction. It explains that an electromotive force (emf) is induced in a conductor when it moves through a magnetic field. The direction of the induced current is determined by Lenz's law, which states that the induced emf will oppose the change in magnetic flux that creates it. Faraday's law quantifies the relationship between the induced emf and the rate of change of the magnetic flux through the conductor.
1) Gravitational and electric fields can be described by their field strength, which is defined as the force exerted per unit mass or charge.
2) Coulomb's law and Newton's law of gravitation describe the relationship between field strength and distance from the source of the field. Field strength decreases with the inverse square of the distance.
3) Electric and gravitational potential are scalar quantities that represent the potential energy per unit mass or charge. Potential increases as distance from the source decreases. Equipotential lines represent regions of constant potential.
Electric fields arise from electric charges and can be represented by electric field lines. A positive test charge experiences a force when placed in an electric field, allowing the field strength to be calculated. The field is strongest closest to the charged object and decreases with distance. Materials are classified as conductors, insulators or semiconductors based on how easily their electrons can move. Coulomb's law defines the force between two point charges as directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
The document discusses electricity and magnetism, specifically resistance and heating effects of currents. It explains that resistance depends on the material and structure of a conductor, with tungsten filament lamps having high resistance and copper wires having low resistance. It also covers Ohm's law, defining resistance as the ratio of potential difference to current, and how resistors, circuits, and resistor combinations work based on this relationship. Kirchhoff's laws for analyzing electric circuits are also summarized.
This document discusses magnetic fields created by electric currents. It begins by introducing magnetic fields and magnets. It then explains that a current-carrying wire creates a circular magnetic field, as shown by iron filings. The direction of the field depends on the current direction. A flat coil and solenoid also produce magnetic fields, with the solenoid's field resembling that of a bar magnet. Current-carrying wires and charged particles experience forces in magnetic fields according to Fleming's left-hand rule. Parallel wires with the same/opposite currents attract/repel each other due to their magnetic fields. The ampere is defined based on the force between parallel current-carrying wires. Magnetic field strength B is directly
1. Batteries work by using a chemical reaction to create a difference in electrolytic potential between two terminals placed in an electrolyte. This potential difference causes ions to flow from one terminal to the other.
2. Primary cells cannot be recharged, while secondary cells can be recharged by applying an external voltage to reverse the chemical reaction.
3. The electromotive force (EMF) of a source is the electrical potential energy, measured in volts, that is transferred to each coulomb of charge passing through the source. Common examples of sources that provide EMF include dry cells, dynamos, and solar cells.
The document discusses wave behavior and reflection and refraction of waves. It provides examples of reflection at fixed and free boundaries and how this causes inversion or no inversion of pulses. It introduces the law of reflection where the angle of incidence equals the angle of reflection. Refraction is discussed where the speed and wavelength change upon entering a new medium. Snell's law is derived relating the sines of the angles of incidence and refraction to the refractive indices of the media. Total internal reflection at the critical angle is also mentioned.
Standing waves are formed when two waves of equal amplitude and wavelength traveling in opposite directions interfere. A standing wave has points called nodes where the disturbance is always zero, and amplitudes called antinodes. When the frequency is increased, different standing wave patterns called harmonics are formed. The fundamental harmonic has a half wavelength, and higher harmonics have wavelengths that are fractions of the total length. Standing waves can also be produced in open and closed pipes, with the harmonic frequencies following specific patterns in each case.
2. Characteristics of e/m Waves If the charge is accelerated; the magnetic field must be changing, the field depends on the velocity of the charge.
3. Characteristics of e/m Waves If the charge that produces this field is oscillating back and forward; it will generate a periodic wave, similar to that produced in a slinky spring.
4. Characteristics of e/m Waves This electromagnetic wave consists of; a changing electric field that, generates a changing magnetic field that, regenerates the electric field, and so on indefinitely.
5. Characteristics of e/m Waves The wave travels by transferring; energy from the electric field, to the magnetic field, and back again.
6. Characteristics of e/m Waves The fields oscillate at right angles; to each other in the one plane, while the wave moves perpendicularly, to both fields.
8. Characteristics of e/m Waves As the electric field reaches the receiving antenna; it exerts a force on the charges, which causes them to vibrate.
9. Characteristics of e/m Waves The wave then regenerates in the receiving antenna. This means the electrons in the receiving antenna; vibrate in the same manner, as the transmitting antenna.
10. Characteristics of e/m Waves Each vibrating electron; emits an electromagnetic wave, in one plane. The electric field; produced by a radio antenna, is in one direction.
11. Characteristics of e/m Waves If the antenna is vertical; the electric field is vertical. A wave that is orientated in a unique direction; is polarised.
12. Characteristics of e/m Waves This means the receiving antenna; must be orientated in the same plane, as the transmitting antenna. For radio waves; this is also vertical.
13. Characteristics of e/m Waves All electromagnetic waves travel at the speed of light. From previous work; the speed of a wave can be related to its frequency and wavelength by: v = f
14. Application - LADS Laser beam is directed onto ocean Two reflected beams are detected One from surface of water and one from surface of ocean The time taken for a pulse of laser light; to complete a round trip from the surface of the water, to the bottom and back again.
15. Application - LADS Knowing the speed at which the wave travels; measuring the time taken, allows us to calculate the distance travelled. S=Δv.t But depth = 1/2s
16. Application - LADS To increase the amount of area the LADS system can cover at one time; laser pulse scans across the path of the aircraft, in the green region of the spectrum.
17. Application - LADS The laser itself is very powerful; (1 MW). This compares to the school laser; 0.95 mW. The laser has both infra red beam (for height above water) and green beam (for depth of sea) The reasons the laser is so powerful include:
23. COHERENCE Coherence - two wave sources that are… Same frequency Same wavelength Maintain a constant phase relationship.
24. Incandescent light Light generated by heating a source is from oscillating charged particles. This will be in a continuous spectrum of frequencies The em waves that result are of same frequency and therefore monochromatic But have no fixed phase relationship
25. INTERFERENCE INTERFERENCE - occurs when two or more waves pass through the same space. CONSTRUCTIVE INTERFERENCE - two waves that have the same phase relationship and frequency. Example: Two waves that have overlapping crests leads to a doubling of the amplitude of the wave.
26. INTERFERENCE DESTRUCTIVE INTERFERENCE - two waves are out of step. Example: One waves crest meets another waves trough. The waves will cancel each other out. Wave Interference Example
27. INTERFERENCE A constant phase relationship is maintained in both constructive and destructive interference when the frequency of both waves is the same. We therefore say that the two sources that produced the waves are mutually coherent.
28. WATER WAVE INTERFERENCE Here is an example of two water waves interfering with each other. The two dippers are striking the water at the same time with the same frequency at S1 and S2.
29. WATER WAVE INTERFERENCE The Law of Superposition applies (sum of all waves added at a particular point). Constructive Interference (crest meets crest or trough meets trough) - waves in phase and reinforcement occurs. Resultant wave has twice the amplitude. Destructive Interference (crest meets trough) - waves half step out of phase and annulment occurs. Zero amplitude.
30. WATER WAVE INTERFERENCE As the two waves have the same frequency they will have a constant phase relationship (coherence). They therefore will have points that will always constructively interfere (ANTINODES) and destructively interfere (NODES).
31. WATER WAVE INTERFERENCE The nodes on the diagram are open circles. The antinodes are shown as black dots.
32. WATER WAVE INTERFERENCE For a point to be on a nodal line, the difference between its distance from one source and the distance from the other source must be an odd number of half wavelengths. This is called the Geometric Path Difference (G.P.D.)
33. WATER WAVE INTERFERENCE For any point on an antinodal line, the G.P.D. must be an even number of half -wavelengths. Reinforcement (antinodes) will occur at G.P.D. = m m = 0, 1, 2…..
34. WATER WAVE INTERFERENCE What if we were to reverse the phase of one source? A crest leaves S1 at the same time as a trough leaves S2. Annulment… G.P.D. = m Reinforcement … G.P.D = (m + ½)
35. LIGHT INTERFERENCE In the case of light, it is the overlapping electromagnetic waves that produce the interference patterns. It is difficult to observe interference patterns with light due its very small wavelength of around The bandwidth would be extremely small (anti nodes close together).
36. LIGHT INTERFERENCE A single slit is illuminated with monochromatic (light of all the same frequency) light. It might be all blue light or all red light. This slit becomes a point source and emits circular wavefronts. The light emerging from the slit is coherent (only one crest or trough can get through at any given time).
37. LIGHT INTERFERENCE If the double slits are equidistant from the single slit, a crest (or trough) will reach the double slits simultaneously.
38. LIGHT INTERFERENCE A sodium vapour lamp would be a good monochromatic light source if using the Young’s Slits Experiment. If you are using a LASER there is no need for the single slit as LASER light is already monochromatic and coherent.
39. LIGHT INTERFERENCE If you were to shine the double slit towards a white screen you would see alternating bands of bright and dark fringes on the screen. The bright bands would be antinodal lines, places where two crests (or troughs) were overlapping.
40. LIGHT INTERFERENCE THE DERIVATION OF d sin = m This is an essential derivation from the syllabus. d = distance between the two slits. L = distance between the slits and the screen. y = the bandwidth (distance between consecutive antinodes or consecutive nodes). Optical Path Difference (O.P.D.) = the extra difference that one of the slits is from the screen.
42. LIGHT INTERFERENCE bisects the angle by the two waves that meet at . is at right angles to in order that we have which is the extra distance or the O.P.D. between the waves.
43. LIGHT INTERFERENCE Since is very small, the angle is approximately . This means that triangle can be treated as a right angled triangle sin = or = d sin Remember that is the Optical Path Difference.
46. DIFFRACTION Diffraction is the bending of a wave as it passes near an obstacle while remaining in the same medium. This phenomena occurs in water, sound and light waves.
47. DIFFRACTION As the slit width approaches the wavelength of the water wave, the diffraction is very noticeable.
48. DIFFRACTION If light passes through an opening that is wide compared to the wavelength, the diffraction effect is small. The result is that we see a sharp shadow.
49. DIFFRACTION If the opening width approaches the wavelength of the light, the diffraction produced becomes more pronounced and the shadow becomes more fuzzy around the edges. The light is diffracted by the thin slit.
50. DIFFRACTION This can also happen when radio waves pass between two large objects. Consider two large buildings in the centre of Adelaide. FM Waves have a wavelength of 2-3 m. They therefore pass through the space between buildings with little diffraction.
51. DIFFRACTION AM Radio waves have a much longer wavelength (200-300 metres). It is at least as large as the gap between the buildings. They therefore show considerable diffraction This allows you to get good AM reception while the FM reception has “shadow zones” in cities.
52. DIFFRACTION Streetlights viewed through a dirty windscreen at night will show a diffraction pattern in the form of a cross. This is due to the fine dust particles having a very small gap between them.
53. MULTIPLE SLIT DIFFRACTION The characteristics of multiple slits can be summarised as below: Interference fringes are superimposed on the single slit diffraction pattern only when there are least two slits enabling the interference of waves to occur.
54. MULTIPLE SLIT DIFFRACTION As the number of slits increases, the diffraction pattern spreads and the intensity of each reinforcement diminishes. As the number of slits increases, each fringe becomes narrower. This results in sharper reinforcement bands.
55. MULTIPLE SLIT DIFFRACTION The central bandwidth is no longer twice that of fringe bands. The bandwidth equation can no longer be used. When there are a large number of slits, very sharp reinforcement lines occur with non-uniform spacing between them.
56. THE DIFFRACTION GRATING A large number of equally spaced parallel slits which can also be called an ‘interference grating’. There are two types: TRANSMISSION: Large number of equally spaced scratches (6000 per cm is common) are inscribed mechanically into a transparent material such as glass. Each scratch becomes an opaque line and the space in between becomes a slit.
57. THE DIFFRACTION GRATING Coherent light is directed on the diffraction grating by passing light through a collimator (light gatherer). The pattern can be seen through the telescope. The whole arrangement is called a spectrometer.
58. THE DIFFRACTION GRATING The pattern is similar to Young’s double slit pattern. The slits are narrow enough so that diffraction by each of them spreads light over a very wide angle on to a screen. Interference occurs with light waves from all slits.
59.
60. THE DIFFRACTION GRATING We use the Spectroscope to find the wavelengths of the different colours. For reinforcement Each wavelength of light (or different colour) will have a unique angle that it is diffracted to on the screen.
61. THE DIFFRACTION GRATING When m = 0, the central reinforcement line is produced and is called the zero order maximum. First order maxima occur when m = 1 and second order maxima when m = 2.
62. THE DIFFRACTION GRATING The diffraction pattern for a grating is different to that from a double slit pattern. The bright maxima are much narrower and brighter for a grating.
63.
64. THE DIFFRACTION GRATING For a grating, the waves from two adjacent slits will not be significantly out of phase but those from a slit maybe 500 away, may be exactly out of phase. Nearly all the light will cancel out in pairs this way. The more lines, the sharper the peaks will be. Double Slit Multiple Slits
65. PRODUCING SPECTRUMS PRODUCING SPECTRUMS FROM WHITE LIGHT USING A SPECTROSCOPE. If the light is not monochromatic, the angles at which the wavelengths produce their mth order maxima are different.
66. PRODUCING SPECTRUMS On either side after the central white maxima and an area of darkness, violet reinforces first as it has the smallest wavelength, then the other colours through to red. A clear first order (m = 1) continuous spectrum can be seen.
67. PRODUCING SPECTRUMS Higher order spectra become spread further and become less intense. The pattern will overlap from the third order onwards and the bandwidth formula used in the double slit cannot be used.
69. LASERS The light from these sources is perfectly coherent and is produced by a process known as Light Amplification by Stimulated Emission of Radiation (LASER). The full explanation of a laser can only be given with quantum theory.
70. LASERS The atoms of (for example) a He - Ne gas laser are optically stimulated to emit light all of the same frequency and in such a way that the waves emitted are in phase with each other.
71. LASERS The emitted light gains in intensity by being reflected many times through the active material which is being stimulated, and then being released from the laser through a partially reflecting end mirror. The resultant beam is highly monochromatic, coherent, intense and unidirectional.
72. LASERS Often, the laser light appears to be speckled when shone onto a screen or wall (such as in one of the year 12 practicals). Speckle is produced whenever a laser beam is reflected by a rough surface. It is due to the interference between light reflected in different directions from the surface.
73. LASERS This is interference due to reflection (several waves combining for amplification)
74. APPLICATION-COMPACT DISCS (CD’S) A CD is a fairly simple piece of plastic about 1.2 mm thick. The CD consists of a moulded piece of plastic that is impressed with microscopic bumps arranged as a single, continuous spiral track of data. A thin, reflective aluminium layer is placed onto the top of the disc, to cover the bumps.
75. APPLICATION-COMPACT DISCS (CD’S) A thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic.
78. APPLICATION-COMPACT DISCS (CD’S) A very important point is that the height of the “bumps” is approximately one quarter the wavelength of the laser light. When the laser light is passing over the “land”, all of the light is reflected off and it travels back to photoelectric cell. The photoelectric cell then produces an electric current.
79. APPLICATION-COMPACT DISCS (CD’S) This electric current then goes on to generate sound in a loudspeaker (see loudspeaker application). Now lets look at what happens when the laser light approaches a “bump”. When the light reaches a bump, half of the light is reflected off the “bump” and half of the light is reflected off the “land”.
81. APPLICATION-COMPACT DISCS (CD’S) Because the bump is ¼ of a wavelength in height, the light being reflected off the land travels one half a wavelength further. The light reaching the photoelectric cell coming from the “land” and the “bump” is out of phase. This leads to partial cancellation and a decrease in intensity. This leads to decreased current being produced.
82. APPLICATION-COMPACT DISCS (CD’S) As the laser moves along the track the intensity of the light falling on the photoelectric cell changes every time it comes into approaches or leaves a bump. It is this change in intensity which causes the fluctuation in electric current, which causes the movement of the loudspeaker and ultimately the fluctuation in sound.
83. APPLICATION-COMPACT DISCS (CD’S) USING INTERFERENCE TO KEEP A LASER ON TRACK The musical data on the CD is read from the inside out. The CD spins above the laser. After one revolution, the laser must move to the outside exactly 1.6 microns to remain on track.
84. APPLICATION-COMPACT DISCS (CD’S) When the monochromatic light passes through the diffraction grating a central beam and a first order diffracted beam will land on the CD.
85. APPLICATION-COMPACT DISCS (CD’S) The central beam is focused on the track of the CD and passes over the bumps while the two first order diffracted beams are focused on the land on either side of the bumps. One diffracted beam is slightly ahead of the other.
86. APPLICATION-COMPACT DISCS (CD’S) The laser beam is tracking correctly when the central beam is varying in intensity from 35% to 100% and the two diffracted beams have a constant intensity of 100%.
87. APPLICATION-COMPACT DISCS (CD’S) If the laser beam were to stray to the other side of its correct position, then the variation in intensity of the main beam is again reduced. The TRAILING beam will now have a reduction in intensity. The tracking mechanism “senses” that it must adjust its position up in order to get back on track.
89. THE QUANTUM HYPOTHESIS Classical (wave) physics could not explain the energy distribution of radiation emitted from a hot object. Objects when heated become red hot. With further heating it turns white hot then blue. The hotter an object becomes, the shorter the wavelength (and the higher f).
90. THE QUANTUM HYPOTHESIS The actual energy distribution is a curve (a), while wave theory predicts (b).
91. THE QUANTUM HYPOTHESIS Planck derived an expression that was in agreement with the results. He was the first to come up with light behaving like a particle. His idea was that the atomic oscillators in a heated material could oscillate with only certain discrete amounts of energy. Light also comes in “discrete packages” or quanta. A quanta of light is called a PHOTON.
92. THE QUANTUM HYPOTHESIS Planck also assumed the minimum energy of vibration E, is proportional to the natural frequency of vibration, f. If the atomic oscillator (electron) is offered less than this amount, it will accept none of the energy. The electron would not go up an energy level. If it is offered enough energy, it will accept only one photon at a time and quickly re-radiate this energy as an identical photon of e-m radiation. The re-radiated energy occurs as the atomic oscillator drops back to one of its permitted energy states.
93. THE QUANTUM HYPOTHESIS The equation for this is: E= hf h is Planck’s constant = 6.625 x 10-34 Js The small number in this constant ensures that a photon will represent a very small amount of light energy.
94.
95. As we dim the light source, the image of the interference pattern would become fainter.
96.
97. LOW INTENSITY LIGHT AND IMAGE BUILDUP … we get the following photographic image. This is the interference pattern! Thus it appears that the build up of an image is caused by the arrival at the plate of localised bundles of light energy.
98. LOW INTENSITY LIGHT AND IMAGE BUILDUP As more and more of these little bundles of light energy arrive at the screen the image is gradually built up. These little bundles of light energy are the PHOTONS. This is an excellent experiment that suggests that light has BOTH WAVE LIKE AND PARTICLE LIKE PROPERTIES.
99. CLASSICAL THEORY CLASSICAL PREDICTION: The more intense the light, the greater the kinetic energy of ejection of the electron. Bright light would eject electrons at high speed ACTUAL OBSERVATION: Intensity (brightness) led to a greater numbers of electrons being ejected from the metal.
100. CLASSICAL THEORY CLASSICAL PREDICTION: More photoelectrons should be ejected by low frequency radiation (i.e. red) than by high frequency radiation. Low frequency waves allow more time for the electron to move in one direction before the field reverses and the electron moves in the opposite direction. ACTUAL OBSERVATION: Experiments showed that high frequency (UV) radiation ejected photoelectrons more readily than low frequency. There was a minimum frequency below which no photoelectrons were ejected.
101. CLASSICAL THEORY CLASSICAL PREDICTION: There should be a time delay between when a radiation is incident on a surface and when the photoelectrons are ejected ACTUAL OBSERVATION: Photoelectrons were ejected instantaneously.
102. CLASSICAL THEORY CLASSICAL PREDICTION: The radiation’s wavefront falls over the whole surface, billions of photoelectrons should be simultaneously ejected. ACTUAL OBSERVATION: By limiting the amount of light on a surface, a single electron could be ejected.
103. CLASSICAL THEORY CLASSICAL PREDICTION: One velocity of ejection should be possible for radiation of one frequency. ACTUAL OBSERVATION: Emitted photoelectrons have a range of ejection velocities and energies.
104. PHOTOELECTRIC EFFECT The observations made on the previous slides do NOT AGREE with the predictions made by the Classical Theory. Photoelectric Effect - Changing Variables Photoelectric Effect - Changing Variables 2 How can we resolve this?
105. QUANTUM (MODERN) PHYSICS ACTUAL OBSERVATION: The (kinetic) energy of ejected photoelectrons is independent of the intensity of radiation. QUANTUM EXPLANATION: A greater intensity means that more photons will fall on the surface. This will simply eject more electrons but NOT at a faster speed.
106. QUANTUM (MODERN) PHYSICS ACTUAL OBSERVATION: Photoelectrons are more likely to be ejected by high frequency than low frequency radiation. QUANTUM EXPLANATION: The energy of a photon depends on the frequency of radiation (E = hf). A high frequency photon is more likely to have greater energy than the work function.
107. QUANTUM (MODERN) PHYSICS ACTUAL OBSERVATION: Photoelectrons are ejected instantly. QUANTUM EXPLANATION: All of the energy of the photon is given up to the electron instantly. Experimental results show that the maximum time delay for the photoelectric effect is about 10-8s.
108. QUANTUM (MODERN) PHYSICS ACTUAL OBSERVATION: A range of electron velocities of ejection are possible. QUANTUM EXPLANATION: Once the work function is subtracted, the remaining energy exists as kinetic energy. Depending on which electron absorbs the photon, varying amounts of kinetic energy may be left over.
109. PLANCK’S CONSTANT This is a diagram of an apparatus used to investigate the characteristics of photoelectric emission. It is used to try to determine Plank’s Constant (h) from E =hf
110. PLANCK’S CONSTANT The cathode (negative) and anode (positive) are sealed in an evacuated glass tube to reduce the impedance (number of collisions) of the photoelectrons reaching the anode. When the light strikes the cathode it causes photoelectrons to be emitted.
111. PLANCK’S CONSTANT If they cross the gap then they will create a current that will be read by a microammeter. The anode is made progressively more positive attracting more photoelectrons until the saturation current is reached.
112. PLANCK’S CONSTANT This means that there cannot be more electrons given out from the cathode. It is attracting all of the electrons being given off at the cathode.
113. PLANCK’S CONSTANT Note that we DO NOT vary the frequency or the intensity during the time that we are making the anode more positive. During this time the current will get stronger, proof that the electrons are being emitted with different kinetic energies.
114. PLANCK’S CONSTANT Only when you make the anode very positive do you finally attract the electrons that have very little kinetic energy (they are drifting around) due to the fact that they required a large amount of energy just to free them (their Work Function).
115. PLANCK’S CONSTANT If the anode is made negative, electrons are repelled until there is no anode current. When the current is zero, the voltage applied is called the stopping voltage (Vs).
116. PLANCK’S CONSTANT At this point even the most energetic electron (with the smallest work function and hence the most kinetic energy) will not be able to make it to the anode (due to repulsion).
117. PLANCK’S CONSTANT The most energetic electron can be written as: K (max.) = Vse = hf- W Where Vse = Joules of energy This can be rewritten as:
119. PLANCK’S CONSTANT This graph shows what happens as we change the frequency (colour) of the light and the voltage required to stop the most energetic electron for that particular frequency.
120. PLANCK’S CONSTANT If the metal is changed, the work function will change but the slope will remain constant. Hence, the threshold frequency will also change.
122. X-RAYS The voltages used were in the range of 30 to 150 kV. The tube is made of heat resistant glass and is evacuated. A step-down transformer converts household voltage to voltages capable of heating a filament to produce thermoelectrons. The collimating hood turns these electrons into a beam that is accelerated by a voltage of at least 10,000V.
124. X-RAYS This produces a continuous spectrum of x-ray frequencies. The graph shows all the possible values of the emitted frequency as a continuous curve with a maximum cut off value.
125. X-RAYS The electron which collides directly with a nucleus gives up all its energy to produce a photon with energy E = hfmax or hc/ min This continuous radiation is called Bremsstrahlung (German for ‘braking’) radiation. It is also called the “soft” x-rays.
127. X-RAYS These are also called the hard x-rays. The high intensity lines (hard x-rays) are the result of bombarding electrons colliding with inner shell electrons. The shells in an atom are called the K, L, M, N etc, shells with K being the innermost. An electron in each shell can have only a certain amount of energy. DE-excitation involves the electron falling back to fill the hole and losing energy. This energy is lost in the form of a photon that is in the frequency range of an x-ray. This makes the hard x-ray for one frequency
128. THE LINE SPECTRUM Derivation of fmax = eV/h Emax of X-ray photon = loss of Kmax of electron hitting the target = Work done by E field in accel. voltage Thus hfmax = e V fmax = eV/h
129. INCREASING THE VOLTAGE If the accelerating voltage is increased, the energy of the colliding electrons is increased and the maximum frequency of the photon increases. The position of the spectral lines for that target material does not alter since the energy levels of the shells are unaffected.
130. INCREASING THE VOLTAGE Notice that the highest intensity also moves to the right. Intensity is just a measure of the number of photons being released for that particular frequency.
131. INCREASING THE CURRENT If the filament current is increased, more thermoelectrons are liberated and so more X-ray photons are also liberated. This increases the intensity but does not alter the spectral lines or the max. frequency which is voltage dependent.
132. APPLICATION: X-RAYS INMEDICINE X -rays have been used as a diagnostic tool almost since Roentgen’s original discovery nearly 100 years ago. They are useful due to their great penetrating power which allows them to cast shadows, to varying degrees, of internal body parts.
135. APPLICATION: X-RAYS INMEDICINE X-rays pass through glass without any significant refraction. This means other techniques must be used. The X-ray film is put into a light proof cassette which is placed at right angles to the beam on the opposite side of the patient from the X-ray source. Shadows are then cast on the film. For sharp shadows, the beam must be point like and the distance between the patient and the film must be small. On a typical X-ray, the dark areas allow the X-rays to pass through the tissue to the X-ray film and so expose the film.
136. APPLICATION: X-RAYS INMEDICINE The light areas, such as bone, leave a shadow. As the beam is uniform, the difference in exposure is due to the different amounts of attenuation (reduction in intensity). The attenuation varies depending on the thickness and type of tissue.
137. APPLICATION: X-RAYS INMEDICINE Effect of Tissue Type Two properties of tissue have an effect on X-ray attenuation: Density-Attenuation is proportional to tissue density. This is useful for X-rays of bones but also for looking at soft tissue. Lung and muscle tissue are chemically similar but lung tissue is only about one third as dense as muscle.
138. APPLICATION: X-RAYS INMEDICINE A beam passing through lung tissue is only attenuated about one third as much as muscle tissue for the same thickness. Bone is about 1.7 times the density of muscle and although the attenuation is greater, it is not attenuated 1.7 times greater. This is because they are not chemically similar and leads into the second reason.
139. APPLICATION: X-RAYS INMEDICINE Atomic Number-As tissue is not composed of pure elements, ‘effective atomic number’ is used. The attenuation increases with atomic number (to the fourth power). As bone has an effective atomic number of 12 compared to lung tissue (7.6) a greater attenuation of X-rays for bone can be expected than to density alone.
140. APPLICATION: X-RAYS INMEDICINE Penetrating Power (Hardness) of X-rays: In general, to achieve good detail of bone tissue, it is necessary to use X-rays with greater penetrating power than for soft tissue for the same thickness. To do this, X-ray photons of greater energy are required.
141. APPLICATION: X-RAYS INMEDICINE the maximum energy of a X-ray is given by e where is the P.D. To produce X-ray photons of greater energy, a greater P.D. is required. Some X-ray machines use AC and so refers to peak value. Modern diagnostic X-ray machines use between about 50 kV and 125 kV.
142. APPLICATION: X-RAYS INMEDICINE The table below shows the percentage transmission through a thickness of 1 cm for different tissue types.
143. APPLICATION: X-RAYS INMEDICINE Exposure Time In taking an X-ray, the required hardness is first determined depending on the tissue type and the thickness of the tissue. This sets the P.D. (known to radiographers as the ‘peak kilovoltage’, kVp). The exposure time is then set. The shorter the time, the less likely the patient will move and blur the image.
146. WAVE BEHAVIOUR OF PARTICLES DE BROGLIE’S HYPOTHESIS Count Louis de Broglie (1892 - 1970) believed in the symmetry of nature. In 1923 he reasoned that if a photon could behave like a particle, then a particle could behave as a wave.
147. WAVE BEHAVIOUR OF PARTICLES He turned Compton’s relationship to make wavelength the subject of the equation. Compton- “a photon has momentum” De Broglie- “An electron has a wavelength”
148. WAVE BEHAVIOUR OF PARTICLES An electron creates a larger wavelength than a macroscopic object due to the fact that it has a very small mass. The wavelength of an electron is very similar to the wavelength of an x-ray. A beam of electrons should then be able to be diffracted, proving that they have wave like properties.
149. WAVE BEHAVIOUR OF PARTICLES This wavelength can be measured using a crystal diffraction grating as mentioned previously as the spacing of the atoms in the crystal is in the order of 10-10m. These waves are not caused by the particle but are connected with its motion. The wavelengths are 1000 x smaller than visible light. Electron beams in electron microscopes are used as they have greater resolving powers and hence greater magnification.
150. DAVISSON-GERMER EXPERIMENT Electrons were allowed to strike a nickel crystal. The intensity of the scattered electrons is measured for various angles for a range of accelerating voltages.
151. DAVISSON-GERMER EXPERIMENT It was found that a strong ‘reflection’ was found at θ = 50° when V = 54V. This appeared to be a place of constructive interference, suggesting that the “matter waves” from the electrons were striking the crystal lattice and diffracting into an interference pattern.
152. DAVISSON-GERMER EXPERIMENT The interatomic spacing of Nickel is close to the ‘wavelength’ of an electron. Therefore it would seem possible that electron matter waves could be diffracted. Davisson and Germer set out to verify that the electrons were behaving like a wave using the following calculations.
155. DAVISSON-GERMER EXPERIMENT Experimental Result (according to Davisson-Germer) X-ray diffraction had already shown the interatomic distance was 0.215 nm for nickel. Since θ = 50°, the angle of incidence to the reflecting crystal planes in the nickel crystal is 25°as shown below:
157. DAVISSON-GERMER EXPERIMENT dsin θ = mλ For the first order reinforcement… λ = dsinθ = (.215 x 10-9)(sin50°) = 1.65 x 10-10 m
158. DAVISSON-GERMER EXPERIMENT The close correspondence between the theoretical prediction for the wavelength by de Broglie (1.67 x 10-10 m) and the experimental results of Davidson-Germer (1.65 x 10-10 m) provided a strong argument for the de Broglie hypothesis.
159. APPLICATION – ELECTRON MICROSCOPES LIGHT MICROSCOPES A normal light microscope is based on at least two converging lenses, the objective and the eyepiece. There is a limit to how much the conventional microscope can magnify the image. This is due to diffraction.
160. APPLICATION – ELECTRON MICROSCOPES This determines the minimum distance between two points on the object that can be distinguished as separate. Instead of coming to a focus at a point, the light focuses to a small disc. Any attempt to increase the magnification just magnifies the diffraction disc. For light microscopy, the minimum distance, using light of wavelength of about 5 x 10-7 m, is about 2 x 10-7 m. This corresponds to a magnification of about 1000. Using ultraviolet light, the magnification can be increased to 3000 x.
162. APPLICATION – ELECTRON MICROSCOPES Once the wavelike properties of electrons were discovered, people realised that they had the properties that were required for high magnification; 1) they have a small wavelength and 2) they can be focused using electric or magnetic fields. Just as an X-ray tube can produce electrons, electrons can be produced for an electron microscope in the same manner by accelerating of electrons across a large P.D. This takes place in an electron gun with P.D.’s in the range of 40 kV to 100 kV.
163. APPLICATION – ELECTRON MICROSCOPES The work done by the electric field and assuming the electrons start from rest, their kinetic energy is given by qV. In the case where the accelerating potential is 60 KV, the kinetic energy is: K = qV = (1.6 x 10-19) x (60 x 103) = 9.60 x 10-15 J. To determine the wavelength of the electrons, the de Broglie relationship is used, = h/p. The momentum must first be determined from the kinetic energy: K = ½mv2 = ½m2v2/m = p2/2m
164. APPLICATION – ELECTRON MICROSCOPES And so the momentum can be determined by: P = = P = 1.32 x 10-22 kgms-1