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# P6 lesson part one

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### P6 lesson part one

1. 1. P6 Wave model of radiation Route map Over the next 12 lessons you will study : Friday 21 October 2011 P6.1 What is a Wave ? P6.2 Describing waves P6.3 Wave properties P6.4 Radiation and waves End of module test P6.5 Bending light beams P6.6 Electromagnetic waves P6.7 Above visible light P6.8 Below the visible light P6.9 Radio waves P6.10 How radio works P6.11 Going digital P6.12 Radiation from space
2. 2. P6.1 What is a wave ? Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand how waves travel through a medium </li></ul><ul><li>Understand that there are two main types of waves transverse and longitudinal </li></ul>We will focus on. Friday 21 October 2011 First activity: Draw a diagram of a wave and label a crest and a trough, and the wavelength and amplitude. Literacy: Wave, wave length, amplitude, frequency, wave speed, vibration, longitudinal wave, transverse wave, medium and light wave. Numeracy: Any wave whether it is transverse or longitudinal can have a frequency (hertz) and wavelength (metres) In transverse waves the vibrations are at 90 o to the direction of travel in longitudinal waves the vibrations are along the same direction. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on how waves transfer energy from one place to another without transferring any matter. Team workers Effective participators Self managers
3. 3. P6.1 What is a wave ? Extension questions: 1: Sound is a longitudinal wave. Give two sources of sound waves ? 2: Light is a transverse wave. Give two sources of light waves ? 3: Look at the properties of both wave types, how do transverse waves differ from longitudinal waves ? 4: Draw a diagram of a longitudinal sound wave and label its crest and trough, the wavelength and the amplitude ? 5: Explain what the frequency of a wave means ? Know this: a: Know that waves transfer energy from one place to another without transferring matter. b: Know that there are two types of waves longitudinal and transverse. Friday 21 October 2011 Introduction: A wave is a vibration moving through a medium or material. A wave transfers energy from one place to another without transferring any matter or particles. There are two main types of waves. Transverse waves have sideways vibrations examples include light and all electromagnetic waves, ripples on water, waves on strings and a slinky wiggled up and down. Longitudinal waves have vibrations along the same line examples include sound waves, seismic waves and a slinky when you push the end. Waves have amplitude, wavelength and frequency. Amplitude is the displacement from the rest position to the crest or trough. Wavelength is the of a full cycle of the wave e.g. From crest to crest. Frequency is the number of complete waves passing a certain point per second.
4. 4. Key concepts P6.1 a Look at the photograph and information and answer all the questions: Longitudinal waves travel from the source in waves of compression, parallel to the direction of the moving wave. Sound waves are longitudinal waves. Transverse waves travels from the source at right angles to the direction of the wave. Light waves are transverse waves. The pitch of sound is determined by the frequency and the volume is determined by the amplitude What children’s toy could you use to model both longitudinal and transverse waves ? Explain how you would measure the wavelength of a) longitudinal wave and b) a transverse wave ? Waves or ripples on a pond is a good model for which type of waves ? Direction of wave Direction of wave Longitudinal waves Transverse wave
5. 5. Key concepts P6.1 b Look at the photograph and information and answer all the questions: Sound is a longitudinal waves and will travel out in all directions form a single source. Loud speaker creates sound by vibrating a membrane and this cause little compression pulses in the air surrounding the speaker. These compression pulses travel through the air at approximately 330 metres per second Explain why ripples caused by throwing a stone into a pond is a good model for how sound waves travel through air ? Does the wavelength or amplitude determine the volume of sound ? Do sound waves travel faster or slower through solids when compared to gases like air ? Properties of waves Amplitude midpoint Direction of wave Crest Trough Wavelength
6. 6. P6.1 c Look at the photograph and information and answer all the questions: All sounds are caused by vibrations. As a speaker vibrates, the layer of air next to it vibrates as well. This causes the next layer of air to vibrate and so on. Sound travels through air at about 300 metres per second. Sound waves travel through matter from a point source just like ripples on a pond. Sound waves can also be reflected and refracted just like light. Explain how a) sound waves or vibrations travel from a radio speaker to your ear and b) sound is detected by the inner ear ? Explain why sound travels through liquids and solids much faster than through gases like air ? A tuning fork vibrates back and forth 75 times a second. How many times does a person’s eardrum that picks up the note also vibrate ? Key concepts Noise: caused by a hammer strike Pure note: caused by a tuning fork strike Type of sound
7. 7. P6.1 d Look at the photograph and information and answer all the questions: Ultrasound, has a high frequency and short wavelength. This type of sound cannot be heard and is used to image unborn babies. These high frequency waves are sent in a narrow beam, to be reflected back by the tissue and bone of the developing embryo. The echo is read by detectors which are linked to visual monitor which forms an image of the developing embryo. Explain why ultrasound is used to image the unborn baby rather than x rays ? Ultrasound scanner use a frequency of 10,000,000 Hz. Do you think you can hear the this sound at this frequency ? Ultrasound can also be used to see blood flow around the heart and the major blood arteries. What might a doctor be looking for if your heart was given an ultrasound scan ? Key concepts
8. 8. P6.1 Plenary Lesson summary: volume amplitude wavelength frequency Friday 21 October 2011 Sound waves, can be used to image an objects size, shape and position. Ships or fishing boats use sonar or echo sounding to detect, for example the surface of the sea bed, location of a shoal of fish or the harbour wall (moorings). The echo tells us how far the mooring wall is away from the ship’s hull. This is particularly useful for very large ships. This system is now found in cars to help the driver ‘reverse park.’ How Science Works: For the next lesson, find out about how wave speed, frequency, and wavelength are connected. Preparing for the next lesson: The w _________ is the distance between two successive compressions (crest or troughs). The f ____________ measured in hertz (cycles per second) is the number of complete vibrations in each second. The a________ is the average height of a crest or trough from the midpoint or the undisturbed position. The size of the amplitude determines the v_________ of the sound. Decide whether the following statements are true or false : False True 3: Sound waves are transverse waves ? False True 2: In transverse waves the vibrations are along the wave direction ? False True 1: Waves carry particles from one place to another ?
9. 9. P6.2 Describing waves Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand how to describe the properties of a wave </li></ul><ul><li>Understand what wave speed, frequency, and wavelength mean and how they are related </li></ul>We will focus on. Friday 21 October 2011 First activity: Write down a short definition for the following key words: amplitude, frequency, wavelength ? Numeracy: The speed of light through air is 300,000,000 m/s or 300,000 km/s. It takes light about 8.3 minutes to travel from the Sun to Earth’s surface. The speed of sound through air is a very slow 330 m/s. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on how to work out the speed of a wave as it travels through a medium. Team workers Effective participators Self managers Literacy: Wave, wave length, amplitude, frequency, wave speed, vibration, longitudinal wave, transverse wave, medium and light wave.
10. 10. P6.2 Describing waves Extension questions: 1: What does wave's a) frequency depend on b) a wave’s speed depend on ? 2: If you increase the frequency of waves through a medium, what will happen to their wavelength ? 2: When a brick is dropped into a lake, waves travel outwards at a speed of 2.5 m/s. The wavelength of these waves is 0.1m. Calculate the waves frequency ? 4: If the speed of sound waves were very different for different frequencies, what effect would this have on the sounds we hear ? Know this: a: Know how to describe the properties of waves b: Know the formula which connects the speed, frequency and wavelength of a wave Friday 21 October 2011 Introduction: To fully describe all waves we need to understand: Amplitude :- Is the maximum displacement of a wave from its rest position. It is measured in metres (m). Frequency :- This is the number of waves that pass any point in a medium every second. It is measured in Hertz (Hz). Wave speed :- This is the speed at which each wave crest moves through the medium. It is measured in metres per second (m/s). Wavelength :- This is the length of a complete wave. It is measured in metres (m).
11. 11. Key concepts P6.2 a Look at the photograph and information and answer all the questions: Look at the diagram opposite, it shows a wave with a wave length of 1.5 m and a frequency of 3 Hz. Work out the wave speed of this wave ? Draw the diagram opposite left and show using a different colour a wave with a wave length of 1.0 m and a frequency of 5 Hz ? The frequency of a wave, its wave speed and its wave length are related. This relation is given by the equation below: Wave speed = frequency x wavelength (m/s) (Hz) (m) This means that for two waves travelling at the same speed, if one wave has half the frequency of the other it will have twice the wave length ! Properties of waves Direction of wave time 0 sec 1 sec Wavelength (m) 1.5 1.5 1.5
12. 12. P6.2 b Look at the photograph and information and answer all the questions: Sound travels in waves through gases solids and liquids. It is slowest through gases like air because the particle in air a spaced apart. Sound travel fastest through dense solids like brick and metals. In iron sound travels at 1500 m/s nearly five times as fast as it travel through air. This is because the particles are packed closely together in solids. If sound travels in air at 330 m/s and a cliff face is 165 metres away from you...work out how long it will take for you to hear the echo of what you have just shouted ? Explain why you can tell if a train is approaching a station by putting your ear to the track ? Sound echo Sound wave Speed of sound Speed of sound through different medium slow slow fast If you wanted to sound proof a wall, what type of materials would you use and explain why ? air brick air Key concepts
13. 13. P6.2 c Look at the photograph and information and answer all the questions: A firework exploded into the night sky 1000 metres from you. The time taken for the first loud bang to reach you was 2.9 seconds. This was repeated four times with the times shown in the table below left. Calculate the average time using the four results and from this calculate the speed of sound through air ? Explain how you could improve a) the reliability of this experiment and b) the accuracy of the reading for the time taken for sound to reach the observer ? When you have an event that produces sound and light at the same time, you can calculate the speed of sound as long as you know the distance between the sound source and yourself, for example: when lightning strikes, thunder is produced at the same time although you see the lightning way before you hear the thunder. You can also calculate how far the storm is away from you ! Calculating the speed of sound Speed = time distance Key concepts Expt. 1 2 3 4 Average Time 2.9 3.2 3.3 2.9 ____ ?
14. 14. P6.2 Plenary Lesson summary: Friday 21 October 2011 You are surrounded by sound waves, some of them are from background noise, some from words spoken to you by your friends. Your ears work by converting these sound waves into nerve impulses. Your ear is a collection of tissues that are highly adapted to collect and process these sound waves so you can make sense of sound. How Science Works: Find out about the properties shared by all waves Preparing for the next lesson: The __________ of a wave in hertz, its wave _________ in metres, and its __________ in metres are not independent of each other. There is a _______ between them, which applies to all waves of every kind. link speed wavelength frequency Decide whether the following statements are true or false : False True 3: The length of a complete wave is the wavelength ? False True 2: Wave speed is the speed at which each wave crest moves through a medium ? False True 1: Amplitude is the maximum distance from the crest to the trough ?
15. 15. P6.3 Wave properties Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand that all waves can be reflected, refracted, diffracted and be subjected to interference. </li></ul><ul><li>Understand how waves behave at barriers, boundaries, edges, or obstacles </li></ul>We will focus on. Friday 21 October 2011 First activity: Draw how light is reflected on a plane mirror and label the different parts of the diagram ? Literacy: Wave, sound wave, light wave, wavelength, amplitude, frequency, crest, trough, reflection, refraction, diffraction and interference Numeracy: The angle of reflection (r) is equal to the angle of incidence (i). This means that a wave that an incidence angle of 60 o will have a reflection angle of 60 o . PLTS Independent enquirers Creative thinkers Reflective learners We will focus on how waves behave at barriers, boundaries, edges and obstacles. Team workers Effective participators Self managers
16. 16. P6.3 Extension questions: 1: Draw a single light ray hitting a mirror at 35 o . Show the reflected ray and show the angle of the light ray relative to the mirror ? 2: Do a) light waves and b) sound waves generally travel faster in less dense or more dense substances? 3: Do water waves travel faster in shallow or deeper water ? 4: Explain how water refracts light and explain why a hunter will throw his spear just in front of a fish rather than at the image that he sees ? Know this: a: Know that the angle of reflection (r) of a wave is the same as the angle of incidence (i) b: Know that the narrower the gap, or the longer the wavelength, the more the wave is diffracted. Friday 21 October 2011 Introduction: Reflection :- This is how waves bounces off a surface. The incoming wave makes an angle (i) which is equal to the angle of reflection (r). Refraction :- If waves cross a boundary from a deeper to a shallower region, they are closer together in the shallow region. The frequency of the wave is the same in both regions and so the wavelength is smaller in the shallow region. Diffraction :- When waves hit a barrier, they bend a little at the edge, and travel into the shadow region behind the barrier. This effect is called diffraction. Interference :- When two waves meet, their effects add. If both waves have the same frequency, this causes an interference pattern.
17. 17. P6.3 a Look at the photograph and information and answer all the questions: Reflection is the rebounding of light from a smooth shiny surface. Surfaces like clean glass reflects light back to the observer in parallel rays, called regular reflection, where the angle of incidence is equal to the angle of reflection. Surfaces which are not smooth, for example the uneven surface of a road, diffuses light in all directions. This is called diffuse reflection. Give three differences between an object and the object’s image in a normal plane mirror ? Explain the difference between reflection of light from a smooth surface and reflection from a rough surface ? Name one device that uses a pair of mirrors to help an observer see an object ? Key concepts Mirror 30 o 30 o Object Image Observer
18. 18. P6.3 b Look at the photograph and information and answer all the questions: Refraction is the bending of light waves when they pass from one medium (e.g. air) to another (e.g. glass.) If the speed of light is different in the two media, then light bends from its original path. The amount of bending depends on the material and the angle of entry. When light is slowed down, it will bend towards the normal, when light speeds up it bends away from the normal. Look at the picture above left, why does the hunter throw his spear in front of where he sees the fish swimming ? Does light slow down or speed up as it enters water from air ? List three objects or devices that uses lenses to refract or bend light ? Key concepts Object Image Water Air
19. 19. Key concepts P6.3 c Look at the photograph and information and answer all the questions: Wave interference happens when two waves form two different sources meet. If both waves have the same frequency, this will cause an interference pattern. When a crest or a wave meets the crest of another, they add to make a bigger crest. When a creates of a wave meets a trough of another, the two cancel each other out Look at the picture opposite left. Try and identify where you have double crests and troughs ? In step Out of step Double crest troughs Crest /troughs cancel Interference of waves Car markers like BMW and Mercedes make their engines less noisy by using anti-noise technology. This is where they produce the same noise (but out of step) as the engine. When the waves from the engine meet these waves what will happen ?
20. 20. Key concepts P6.3 d Look at the photograph and information and answer all the questions: Any type of wave can be diffracted. A diffracted wave will &quot;spread out&quot;. Diffraction occurs when the wavelength of a wave is of a similar size to an obstacle or a gap in a barrier. This is ho a harbour wall will protect boats and ships form the energy carried by waves. Inside the harbour only a small fraction of the energy gets to shore. Explain how a harbour wall reduce the amount of wave energy that could lea to damages to boats and ships ? What happens to the wave if you reduced the size of the gap ? Diffraction of waves Look at the picture opposite left. Try and identify what happens when the incoming waves (from left to right) meet the barrier ?
21. 21. P6.3 Plenary Lesson summary: effects diffraction reflected refracted Friday 21 October 2011 The hit Hollywood movie “A perfect storm” staring George Clooney dramatises the loss of the ‘Andrea Gail’ a fishing boat and its crew, off the East coast of America. Huge 40 metre waves sank the ship as the result of two weather systems colliding into one another. The effect of two crests or troughs meeting one another meant that the ship had no chance. A storm system like this happens once every 1000 years ! How Science Works: Research into radiation, models of radiation and light as part of the electromagnetic spectrum. Preparing for the next lesson: When waves bounce off a surface, they are ____________. When waves cross a boundary from a deeper to a shallower region, they are ____________. When waves hit a barrier, they bend a little and are ____________. Interference is when two waves meet and their _________ add up. Decide whether the following statements are true or false : False True 3: Two waves that are in step add to make a bigger disturbance ? False True 2: The angle of reflection (r) is equal to the angle of incidence (i) ? False True 1: Waves travel at different speeds in substances which have different densities ?
22. 22. P6.4 Radiation and waves Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand how we model light and other types of radiation </li></ul><ul><li>Understand the properties of light and the evidence that light behaves like a wave </li></ul>We will focus on. Friday 21 October 2011 First activity: Imagine you were trying to describe the properties of light as a wave. Give details of two things you could say about light that would support your argument ? Literacy: Radiation, wave, electromagnetic spectrum, models, reflection, refraction, diffraction, interference, wave speed, wavelength, frequency and amplitude. Numeracy: All types of electromagnetic radiation travel at exactly the same speed through space, which is a vacuum. That speed is very high – about 300 million m/s. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on nature and some basic properties of light. Team workers Effective participators Self managers
23. 23. P6.4 Radiation and waves Extension questions: 1: List 3 other types of wave found in the em spectrum and give an example of a source for each one e.g infra red remote control ? 2: List three properties of electromagnetic waves ? 3: Sound waves can’t travel through a vacuum, explain why ? 4: Explain how interference patterns produce when light form two source meet provides strong evidence for light as wave ? 5: If infra red waves are absorbed what happens to the absorber ? Know this: a: Know how we can use models to show the properties of light as a wave or stream of particles. b: Know that light is part of electromagnetic waves with similar properties. Friday 21 October 2011 Introduction: There are seven types of electromagnetic waves. Light is a type of electromagnetic wave. It travels out in all directions from a source until it hits another object. It might be reflected (bounce off), transmitted (go through), or absorbed (transfer energy to it), or a combination of all three. When radiation is absorbed, it causes changes in the absorber, which allow us to detect it. Light is reflected and refracted. This is consistent with light being a wave but does not really provide strong evidence, because a stream of particles would also do the same. Interference provides a more conclusive evidence for light as a wave.
24. 24. Key concepts P6.4 a Look at the photograph and information and answer all the questions: Young’s double slit experiment proved that light was a wave rather than a stream of particles. A light source is positioned behind a screen which possesses a pair of closely spaced narrow slits.  Light emerges from the pinholes and spreads as spherical waves; the waves overlap, and a interference pattern is produced. Explain what happens when a) a crest meets a another crest and b) a crest meets a trough ? How did young’s experiment help prove that light was a wave rather than a stream of particles ? A friend tells you that the fact that light can travel through glass and other transparent materials also support the wave model is he right or wrong ? Young’s experiment
25. 25. P6.4 b Look at the photograph and information and answer all the questions: Light waves travel in all directions from a light source like a bulb or the sun. These objects are said to be luminous. Light waves all travel at the same speed and are able to transfer energy. Light waves do not need anything to travel through which is why light can reach us from our Sun and other stars in the Milky Way. Light waves can also be reflected, refracted and dispersed. Describe one experiment you could do to show that light rays transfer energy ? A torch is a source of light...name three other sources of light ? In the picture below left, a shadow of a man has been formed...where is the light source that created this shadow ? Key concepts
26. 26. P6.4 c Look at the photograph and information and answer all the questions: Lasers were first developed in the 1960’s. Laser stands for Light Amplification by Stimulated Emissions of Radiation. Light waves from lasers are all in step and so they give a very powerful beam of light. Lasers are used to cut metal, to stop internal bleeding by sealing broken blood vessels and to read information from DVDs and bar codes. Explain why you should never shine a laser into someone’s eye ? Explain how supermarkets like Tesco and Sainsbury use lasers to read bar codes at the till ? Why are lasers used during operations instead of scalpels...give one advantage ? Key concepts
27. 27. P6.4 Plenary Lesson summary: Friday 21 October 2011 Endoscope medical instruments are used to view inside the human body by inserting the instrument into a natural or created aperture. The endoscope uses a fibre optic bundle or conventional optics to relay the image to the eye or a television camera. It also take light into the body cavity so surgeons can see what they are doing. How Science Works: Research into how light is both reflected and refracted and how optic fibre work by total internal reflection. Look into the use of optic fibres for broadband internet and keyhole surgery. Preparing for the next lesson: All electromagnetic waves travel at exactly the same _______ through a vacuum. Light is part family of wave with similar properties which make up the electromagnetic __________. Light can behave both as a _________ of particles and also as a _________ as shown by interference phenomenon. spectrum wave stream speed Decide whether the following statements are true or false : False True 3: The intensity of e.m. radiation is the energy of the wave delivered per second ? False True 2: The energy of electromagnetic waves depend on the frequency of the wave ? False True 1: Sound waves are part of the electromagnetic waves ?
28. 28. P6.5 Bending light beams Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand what happens to light crossing a boundary between different medium </li></ul><ul><li>Understand about how optical fibres work and total internal reflection </li></ul><ul><li>Understand how white light is dispersed into different colours </li></ul>We will focus on. Friday 21 October 2011 First activity: Briefly write down an explanation for the following terms: reflection, refraction, interference and diffraction. Literacy: Light, electromagnetic spectrum, reflection, refraction, diffraction, absorption, radio waves, microwaves, infra red, UV light, X rays, gamma rays, optical fibres and total internal reflection Numeracy: The speed of light in air is 300,000,000 m/s. When light travels through a transparent object light glass or plastic it slows down and changes direction. The speed of light in glass is 200,000,000 m/s. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on how and why light changes direction when it crosses a boundary. Team workers Effective participators Self managers
29. 29. P6.5 Bending light beams Extension questions: 1: Why does light bend when it crosses a boundary between two different medium like air and glass or air and water ? 2: What is total internal reflection and why does it happen ? 3: Explain how optical fibres use total internal reflection to produce images or carry information for example across the internet ? 4: Briefly explain how white light is split by a prism ? 5: What is an endoscope and what phenomenon does it depend on ? Know this: a: Know that light changes direction and speed when crossing form one material to another. b: Know that total internal reflection happens because light changes direction when it from denser medium to a less dense medium. Friday 21 October 2011 Introduction: Waves travel at different speeds in substances which have different densities. For example, light waves travel more slowly in denser media. Sound waves travel faster in denser substances. In total internal reflection (TIR) all the light is reflected and none refracted. Light travels along optical fibres because of total internal reflection. Light entering one end of a fibre is reflected repeatedly from the sides until it comes out the other end. Optical fibres allow doctors to look inside the body without using surgery. Dispersion is the splitting of white light into a spectrum as it passes through a glass prism.
30. 30. Key concepts P6.5 a Look at the photograph and information and answer all the questions: T When white light is shone through two glass prisms we get dispersal and recombination. When light travels through the first prism it disperses forming a rainbow. When these colour than pass through a second inverted prism it recombines to form white light just like the original source. Rain drops form rainbows in a similar way. They act like mini prisms dispersing light into its 7 colours. Does the colour of light depend on its frequency or wavelength or both ? Dispersion and recombination of light by two prisms Which scientist famously first describe the dispersion of white light into its seven colours ?
31. 31. Key concepts P6.5 b Look at the photograph and information and answer all the questions: Refraction is the bending of a wave when it enters a medium where it's speed is different to that through air. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media. Using the diagram, in glass light is refracted to 34.5 o and in water to 40.5 o ...does light slow down more in water or in glass ? Name two other materials where light is refracted, for example diamond ? Glass Plastic Water 38.2 o 40.5 o 34.5 o
32. 32. P6.5 c Look at the photograph and information and answer all the questions: When light strikes the edge between a material with a high refractive index and another with a low refractive index, the light is totally reflected, remaining inside the material. An optic fibre or endoscope exploits this effect. Light travels in glass around 200,000 kms -1 , meaning that inside a fibre optic cable, it will take less 0.1 of a second to travel from England to Australia. Explain why optic fibres carry information far quicker than conventional copper telephone cable ? Give one use of a doctors endoscope pictured below left ? Optic fibres used to carry information across the internet are covered in a shiny foil...explain why this is necessary ? total internal reflection Key concepts
33. 33. P6.5 Plenary Lesson summary: dense total internal reflection optical fibre Friday 21 October 2011 Optic fibres use light that is totally internally reflected to carry huge amount of data or information at close to the speed of light and all in a fibre that is as thick as a human hair. If a beam of light is sent down a thin glass rod, total internal reflection traps the light inside the rod. Fibre optics finds their use in the medical field too. How Science Works: Research into the properties of electromagnetic waves and their uses, for example infra red, microwaves and X-rays. Preparing for the next lesson: TIR stands for _______ ________ __________. Total internal reflection occurs when a light wave travels from a _______ to a less _______ medium. Light travels along an optical fibre because of ________ ________ _________. _______ _______ enables doctors to look inside the body without using surgery. Decide whether the following statements are true or false : False True 3: During refraction waves change speed and direction ? False True 2: Splitting light into different colours by a prism is called dispersion ? False True 1: Light is refracted because its speed is different in the two media ?
34. 34. P6.6 Electromagnetic waves Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand about the family of waves know as the electromagnetic spectrum </li></ul><ul><li>Understand the properties shared by all electromagnetic waves including radio waves, microwaves, infra red, light, U.V light, X-rays and gamma rays </li></ul>We will focus on. Friday 21 October 2011 Literacy: Electromagnetic spectrum, radio waves, microwaves, infra red, light, UV light, X-rays, gamma rays, energy transfer, speed of light, frequency and wavelength. Numeracy: The Sun is a source of electromagnetic waves including, visible light UV light and infra red. The SUN is 150,000,000 km from Earth. Light and other e.m waves take about 8.3 minutes to reach the Earth from the sun. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on the properties and uses of electromagnetic waves. Team workers Effective participators Self managers First activity: Write down three things you know about waves belonging to the electromagnetic spectrum. It could be a type of wave, its use or a source of that wave ?
35. 35. P6.6 Electromagnetic waves Extension questions: 1: Make a list of the seven electromagnetic waves and indicate how frequency and wavelength varies along the spectrum ? 2: From the list which is the odd one out not belonging to the e.m spectrum: radio, UV. Light Sound and microwaves ? 3: Name a type of electromagnetic radiation which is a) visible to the eye, b) emitted by hot objects and c) emitted by some radioactive materials ? 4: Give a detector for a) infra red b) light, c) x rays and d) radio ? Know this: a: Know that there is a family of waves that are called the electromagnetic spectrum b: Know that the higher the frequency of an electro-magnetic wave, the more energy each photon transfers from the source to the absorber. Friday 21 October 2011 Introduction: Electromagnetic waves consists of seven main waves. These include:- radio waves (long medium and short), microwaves, infra-red, visible light, ultraviolet, x-rays and gamma rays. These waves share similar properties. - They travel through empty space - They travel through space at a speed of 300,000,000 m/s - They are transverse waves - They transfer energy from one place to another. Electromagnetic radiation is always emitted and absorbed in packets called PHOTONS.
36. 36. Key concepts P6.6 a Look at the photograph and information and answer all the questions: How does the a) frequency and b) the wave speed change from radio waves to gamma rays ? Explain what happens to the penetration ability as you move form radio waves to gamma waves ? Doctors exploit the penetrating ability of which wave to examine broken bones ? Electromagnetic waves are transverse waves which travel at a speed of 300,000 kms -1 through a vacuum. This is usually called the speed of light. All e.m waves transfer energy from one place to another and like visible light can be reflected by smooth, hard surface or refracted when they travel form one material to another. through transparent materials. The electromagnetic spectrum 10 -9 m 10 -6 m 10 -3 m 1 10 3 m 10 6 m 10 9 m Photon energy (J) Increasing energy and penetration Photons and the electromagnetic spectrum
37. 37. Key concepts P6.6 b Look at the photograph and information and answer all the questions: <ul><li>Albert Einstein developed the theory that radiation including waves belonging to the electromagnetic spectrum is always emitted and absorbed as packets of energy called photons. He stated that the total amount of energy transfer for a beam of radiation can be calculated by taking into account: </li></ul><ul><li>the energy of each photon </li></ul><ul><li>the number of photons arriving each second on the absorbers surface </li></ul>Look at the two cars opposite, they are identical except their colour. Explain which one will heat up the most on a hot summer’s day ? If both are bathed in the same sunlight explain your answer to the first question in terms of photons and how they are absorbed onto the car’s surface ? photons photons
38. 38. P6.6 Plenary Lesson summary: photon energy intensity number Friday 21 October 2011 Ever wondered why dark coloured materials fade more quickly in the sunshine when compared to lighter coloured materials. Dark coloured materials are good absorbers so receive a greater total amount of energy when compared to lighter materials. So if you want to but a tent and don’t want to have to replace it due to fading, then buy a light or silver coloured tent. How Science Works: Reach into electromagnetic waves that are found above visible light. Look into U.V. light, X-rays and gamma rays, their uses, sources, detectors and dangers as ionising radiation. Preparing for the next lesson: The total amount of ___________ which a beam of radiation transfers each second to the absorber, its ___________ depends on the energy of each ___________ in the beam and the __________ of photons arriving every second. Decide whether the following statements are true or false : False True 3: Light from the Sun takes about 499 seconds to reach Earth’s surface ? False True 2: Albert Einstein first developed the idea that light had mass and form ? False True 1: The energy of a photon depends on the frequency of electromagnetic waves ?