Polarization
The phenomena of interference and diffraction show that light is wave motion but they do not prove whether the waves are transverse or longitudinal. The phenomena of light on which the vibration of light is restricted in a particular plane are called plane polarize light
In another word, the phenomenon which studies the transverse nature of light is known as polarization
Difference between polarized and unpolarized light
| Unpolarized light | Polarized light |
|---|---|
| It vibration of light is possible in all directions with equal amplitude. | The vibration of light is undefined to one plane only. |
| It has more intensity. | It has less intensity. |
Analyzer and Polarizer
1. An analyzer is a device that analyses whether the light is polarized or not.
2. A polarizer is a device that polarizes the light
Polaroids
A device used to produce plane polarize light is called a polaroid.
Polarizing angle
Fig: Polariozing angle
The angle of the incident at which the reflected light is completely polarized is called the polarizing angle.
Brewster's Law
It states that the refractive index of a medium is equal to the tangent of the polarizing angle for the given medium.
i.e μ = tanQp
∴μ = repractive index
Qp = Polarizing angle
Fig: Brewsters Law
Proof
Let AB be the unpolarized incident with angle Qp which incident at point 'B' on 'MN' surface whose refractive index is 'µ' and some portion of ray gets reflected along with BC which is polarized and remaining portion gets refraction along 'Qp' with the angle of refraction 'r'.
Then from Snell's law
Brewster's found at a polarizing angle 'Qp' the angle between reflected light is 90°
So Qp + 90 + r = 180
∴ r = 90-Qp
So, equation (i) becomes ;
Which Proves Brewster law
Transverse nature of light
When ordinary light is passed through a pair of crystals P1 and P2 with their plane at a right angle to the direction of light as shown in figure (a), the intensity is maximum in this position. But when the plane of ‘P2’ is rotated through-plane as shown in figure (b), the intensity is minimum in this case. This shows that light is a transverse wave in nature.
Some useful terms
μ=tanθ P
θP+90+r=180
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