Tag: optics

Questions Related to optics

Making a light wave vibrate in only one plane is known as :

polarisation of light polarisation wave optics optics physics

  1. refraction.

  2. reflection

  3. Interference

  4. diffraction

  5. polarization.

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Correct Option: E
Explanation:

Light in the form of a plane wave in space is said to be linearly polarized. Light is a transverse electromagnetic wave, but natural light is generally unpolarized, all planes of propagation being equally probable. 

The process of making the light wave vibrated in a single plane is known as polarization.

Why do polarized sun glasses block out some reflected light (glare), but do not block out light that has not been reflected?

polarisation of light polarisation wave optics optics physics

  1. Some reflected light is at least partially polarized

  2. Some reflected light changes frequency

  3. Some reflected light is red-shifted

  4. Some reflected light is at least partially diffracted

  5. Some reflected light splits into multiple photons

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Correct Option: A
Explanation:

When ordinary (unpolarised) light is reflected from a surface , it gets partial polarisation , it means some of the electric vectors in some planes are cut-off . When this partially polarized light is incident on polarized glasses , glass acts as an analyser and therefore block out some reflected light .

The polarizing angle of glass is $57^{\circ}$. A ray of light which is incident at this angle will have an angle of refraction as

polarisation of light polarisation wave optics optics physics

  1. $33^{\circ}$

  2. $38^{\circ}$

  3. $25^{\circ}$

  4. $43^{\circ}$

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Correct Option: A
Explanation:

The angle between incident ray and reflected is $21°$ and the angle between reflected and refracted ray is $90°$.

So the angle is $90°-57°=33°$

When a beam of light wavelength $\lambda$ is incident on the surface of a liquid at an angle $\phi$, the reflected ray in completely polarized. The wavelength of light in the liquid medium is

polarisation of light polarisation wave optics optics physics

  1. $\lambda\ tan\phi$

  2. $\dfrac{\lambda}{\tan {\phi}}$

  3. $\dfrac{\lambda}{\cos{\phi}}$

  4. $\dfrac{\lambda}{\sin{\phi}}$

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Correct Option: B

At a time, the image of sun formed due to reflection at air-water interface, is found to be highly polarized. If refractive index of water is $\mu =\dfrac{4}{3}$, then the angle of the sun above the horizon is ?

polarisation of light polarisation wave optics optics physics

  1. $37^{o}$

  2. $53^{o}$

  3. $30^{o}$

  4. $60^{o}$

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Correct Option: A

Two polarising plates have polarising directions parallel, so as to transmit maximum intensity of light. Through what angle must either plate be turned, if the intensities of the transmitted beam is to drop by half.

polarisation of light polarisation wave optics optics physics

  1. $30^{o}$

  2. $45^{o}$

  3. $60^{o}$

  4. $70^{o}$

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Correct Option: B

The velocity of light in air is $3\times 10^{^{8}}m/s$ and in medium is $\sqrt 3 \times 10^{^{8}}m/s$. The Brewster's angle of a medium is:

polarisation of light polarisation wave optics optics physics

  1. $30^{0}$

  2. $60^{0}$

  3. $45^{0}$

  4. NONE

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Correct Option: A
Explanation:
Refractive index $(\mu )$ of the medium is: 
$\mu= \dfrac{c}{v}$ ($v$ :velocity of light in medium)
 using Brewster's law,
 $tan\theta _{B}=\mu $             [$\theta _{B}$: Brewster's angle] 
$\Rightarrow \theta _B=tan^{-1}\left ( \dfrac{c}{v} \right )=tan^{-1}\left ( \dfrac{3\times 10^{8}}{\sqrt{3}\times 10^{8}} \right )$  
$= tan^{-1}\left ( \dfrac{1}{\sqrt{3}} \right )$ 
$\Rightarrow \theta _{B}=30^{o}$

A Polaroid is placed at $45^0$ to an incoming light of intensity $I _0$. Now the intensity of light passing through Polaroid after polarization would be 

polarisation of light polarisation wave optics optics physics

  1. $I _0$

  2. $\displaystyle \dfrac{I _0}{2}$

  3. $\dfrac{{{I _o}}}{4}$

  4. Zero

Show answer
Correct Option: B
Explanation:

Given,

$\theta=45^0$
By malus law,
$I=I _0 cos^2 \theta$
$I=I _0 cos^245^0=I _0 (\dfrac{1}{\sqrt{2}})^2$
$I=\dfrac{I _0}{2}$
The correct option is B.

A ray of unplorised incident on a glass plate at the polarising angle $57^{o}$. Then

polarisation of light polarisation wave optics optics physics

  1. The reflected ray and the transmitted ray both will be completely polarised

  2. The reflected ray will be completely polarised and the transmitted ray will be partially polarised

  3. The reflected ray will be partialy polarised and the transmitted ray will be completely polarised

  4. The replected and transmitted both ray will be partially polarized

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Correct Option: A

The critical angle for a medium is $ 45^o $ What is polarising angle? Angle refraction ?

polarisation of light polarisation wave optics optics physics

  1. $ 34.7^o, 32.3^o $

  2. $ 64.7^o, 30.3^o $

  3. $ 54.7^o, 35.3^o $

  4. $ 44.7^o, 45.3^o $

Show answer
Correct Option: C