The document discusses various properties of light including its nature as both a wave and particle, how it reflects, refracts, and interacts through interference and polarization. It covers key experiments such as Young's double slit experiment that demonstrated light's wavelike properties and the photoelectric effect that showed its particulate nature. The properties of reflection, refraction, dispersion, interference, diffraction, polarization and Brewster's law are also defined and explained in the context of light as an electromagnetic wave.

1. GOOD MORNING

2. Light

3. DEFINITION OF LIGHT
Light is electromagnetic radiation within a certain portion of the electromagnetic
spectrum . The word usually refers to visible light, which is visible to the human eye
and is responsible for the sense of sight . The sun produces light, and that light
bounces off objects and into our eyes. This makes it so that we can see things, because
the brain can interpret that light and tell us what's out there.
Object

4. ELECTROMAGNETIC WAVE
• We know that light is one kind of energy . We can ask now that how light`s energy moves from one
place to another . We can explain the movement of light`s energy by two theory which was given by
Sir Isaac Newton and Huygens . The two theory are “Newton`s particle theory of light and Wave
theory of light”. Now we will see Wave theory of light .
• Wave theory of Light :- According to this theory Light moves from one place to another in wave form
to the Ether .
• Electromagnetic Theory :-The electromagnetic theory is a united theory of electromagnetism
established by James Clerk Maxwell. This theory primarily discusses the relationships between
electric field and magnetic field based from previous observations and experiments related to
electricity, magnetism and optics combined. There are four phenomena involved in this theory . He
was able to develop four equations , which nowadays is called the Maxwell's equation . He was also
able to compute and establish that both electricity and magnetism travel at a constant speed
equivalent to the speed of light. It was, therefore, concluded that the light travel at a constant speed
in all directions. From this theory We know that Light is a one kind of Electromagnetic wave .

5. PROPERTIES OF LIGHT
• Reflection
• Refraction
• Dispersion
• Total Internal Reflection
• Interference
• Diffraction
• Scattering of Light
• Polarization

6. REFLECTION
Light follows the Law of Reflection: “The angle of incidence is equal to the angle of
reflection.”
Light can bounce off materials in two ways:
1. Diffuse reflection – reflected rays go in different directions; happens in rough-
textured or uneven surfaces
2. Regular/Specular reflection – reflected rays go in one directions; happens in
smooth and shiny surfaces .
Diffuse reflection Regular/Specular reflection

7. REFRACTION
Refraction is a bending of wave when it enters a medium where its speed is different . 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 .
That’s mean :-
Light bends/refracts when it changes speed.
This usually happens when the light travels from one medium to the next.
Simple rule of thumb in refraction:
• If light slows down, it will refract towards the normal line.
• If light speeds up, it will refract away from the normal line.

8. REFRACTION
Light travels faster in air, slow in water and slower still in glass.
The slower light is in a medium, the more it refracts/bends in it.
The measure of how much light refracts in a medium is called index of refraction.

9. DISPERSION
• The process in which light is separated into its colors due to the differences in
degrees of refraction.

10. INTERFERENCE
• When two light waves meet or coincide, it can create either constructive or
destructive interference based on how the crests & troughs of the waves meet.

11. COHERENT SOURCE
Two sources are said to be coherent if they have exactly same frequency, and have zero
or constant phase difference. Most of the light sources around us - lamp, sun, candle
etc. are combination of multitude of incoherent sources of light. Laser is a coherent
source i.e. constituent multiple sources inside the laser are phase-locked.

12. Production of Coherent source
By division of
Wave front
By division of
Amplitude

13. PRODUCTION OF COHERENT SOURCE
• By division of Wave front :- In this method the wave – front is divided into two or more
parts by the use of mirrors , lenses and prisms. The well known methods are Young`s
double slit arrangement, Frenel`s biprism and Lloyd's single mirror etc. .
• By division of Amplitude :- In this method the amplitude of the incoming beam is divided
into two or more parts by partial reflection or refraction . These divided parts travel
different paths and finally brought together to produce interference . This type of
interference needs broad source of light . The common example of such interference of
light are the brilliant colors seen when a thin film of transparent material like soap
bubble or thin film of kerosene oil spread on the surface pf water is exposed to broad
source of light .

14. IS LIGHT A WAVE OR A PARTICLE
• Light has a dual nature.
• Depending on the phenomenon or behavior in question, light can be treated either
as a wave or as a particle.
• To examine this wave-particle duality, we will examine two experimental proofs.

15. LIGHT IS A WAVE: YOUNG’S DOUBLE-SLIT
EXPERIMENT
• Conducted by Thomas Young in the early 1800’s
• Provided an experimental basis for considering light as a wave.

16. LIGHT IS A WAVE: YOUNG’S DOUBLE-SLIT
EXPERIMENT

17. LIGHT IS A WAVE: YOUNG’S DOUBLE-SLIT
EXPERIMENT

18. KEY POINTS OF YOUNG’S EXPERIMENT
• The individual slits acted as individual sources which light passes through and
spreads.
• Light exhibits interference which is a wave property.

19. LIGHT IS A PARTICLE: THE
PHOTOELECTRIC EFFECT
• Explained by Einstein during the early 1900’s
• Provided an experimental basis for considering light as a particle.
• Einstein earned a Nobel Prize for his explanation.

20. KEY POINTS OF PHOTOELECTRIC EFFECT
• Higher energy light knocks off electrons at higher energy.
• The number of ejected electrons is directly related to the intensity
(brightness) of light. This means brighter lights emit more photons.
• Light is a particle since it is capable of ‘knocking off’ electrons.
Further, unlike waves, increasing the brightness does not increase the
energy of the knocked off electrons.

21. POLARIZATION OF LIGHT
• Experiments on interference and diffraction have shown that light is a form of wave
motion . These effects do not tell us about the type of wave motion . i.e. whether
the light waves are longitudinal or transverse , or whether the light waves are
linear, circular or torsional .The phenomenon of polarization has helped to establish
beyond doubt that light waves are transverse wave .

22. POLARIZATION BY FILTERING
• Polarization can be understood by considering a rope model of light waves, as shown
in the figure below.
• The transverse mechanical waves in the rope represent transverse light waves. The
slots represent what is referred to as the polarizing axis of the polarizing medium.

23. POLARIZATION BY FILTERING
• When the rope waves are parallel to the slots, they pass through.
• When they are perpendicular to the slots, the waves are blocked.

24. POLARIZATION BY FILTERING
• Polarizing media contain long molecules in which electrons can oscillate, or move back and
forth, all in the same direction.
• As light travels past the molecules, the electrons can absorb light waves that oscillate in
the same direction as the electrons.
• This process allows light waves vibrating in one direction to pass through, while the waves
vibrating in the other direction are absorbed.
• The direction of a polarizing medium perpendicular to the long molecules is called the
polarizing axis.
• Only waves oscillating parallel to that axis can pass through.

25. POLARIZATION BY FILTERING
• Ordinary light actually contains waves vibrating in every direction perpendicular to
its direction of travel.
• If a polarizing medium is placed in a beam of ordinary light, only the components of
the waves in the same direction as the polarizing axis can pass through.
• On average, half of the total light amplitude passes through, thereby reducing the
intensity of the light by half.
• The polarizing medium produces light that is polarized, meaning that it has a single
plane of oscillation.
• Such a medium is said to be a polarizer of light and is called a polarizing filter.

26. MALUS’S LAW
• The law that explains the reduction of light intensity as it passes through a second
polarizing filter is called Malus’s law.
• If the light intensity after the first polarizing filter is I1, then a second polarizing
filter, with its polarizing axis at an angle, θ, relative to the polarizing axis of the
first, will result in a light intensity, I2, that is equal to or less than I1.
Malus’s Law
• The intensity of light coming out of a second polarizing filter is equal to the intensity
of polarized light coming out of a first polarizing filter multiplied by the cosine,
squared, of the angle between the polarizing axes of the two filters.

27. MALUS’S LAW
• Using Malus’s law, you can compare the light intensity coming out of the second
polarizing filter to the light intensity coming out of the first polarizing filter.
• Thereby, you can determine the orientation of the polarizing axis of the first filter
relative to the second filter.
• A polarizing filter that uses Malus’s law to accomplish this is called an analyzer.
• Analyzers can be used to determine the polarization of light coming from any source.

28. BREWSTER LAW

29. BREWSTER LAW

30. All these are some tropics of Light .
Have you any question ?

32. CREATED BY
Md
Touhidul
Islam
Shawan
B.Sc. In CSE
Daffodil
International
University