Tag: wave optics

Questions Related to wave optics

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

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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 $

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Correct Option: C

When sun light is incident on water at an angle of $ 53^o $ the reflected light is found to be completely plane-polarised. Determine : (i) angle of refraction of light,
(ii) refractive index of water.

polarisation of light polarisation wave optics optics physics

  1. (i) $ 31^o $
    (ii) $ 1.427 $

  2. (i) $ 30^o $
    (ii) $ 2.327 $

  3. (i) $ 27^o $
    (ii) $ 1.327 $

  4. (i) $ 37^o $
    (ii) $ 1.327 $

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Correct Option: D

The angle between polariser and analyser is $30 ^ { \circ }$  The ratio of intensity of incident light and transmitted by the analyser is

polarisation of light polarisation wave optics optics physics

  1. 3:4

  2. 4:3

  3. $\sqrt { 3 } : 2$

  4. $2 : \sqrt { 3 }$

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Correct Option: A
Explanation:
Given,
$\theta=30^0$
By using malus law,
$I=I _0cos^2\theta$
$\dfrac{I}{I _0}=(cos30)^2$
$\dfrac{I}{I _0}=(\dfrac{\sqrt{3}}{2})^2=\dfrac{3}{4}$
ratio, $I:I _0=3:4$
The correct option is A.

The angle of incidence of light is equal to Brewster's angle, then 
A) Reflected ray is perpendicular to refracted ray
B) Reflected ray is parallel to refracted ray
C) Reflected light is polarized having its electric vector in the plane of incidence 
D) Refracted light is polarized.

polarisation of light polarisation wave optics optics physics

  1. (A) and (D) are true

  2. (A) and (B) are true

  3. (A) and (C) are true

  4. (B) and (C) are true

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Correct Option: A

A beam of unpolarised light of intensity $I _{0}$ is passed through a polaroid $A$ and then through another polaroid $B$ which is oriented so that its principal plane makes an angle of $45^{\circ}$ relative to that of $A$. The intensity of the emergent light is

polarisation of light polarisation wave optics optics physics

  1. $I _{0}$

  2. $I _{0}/2$

  3. $I _{0}/4$

  4. $I _{0}/8$

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Correct Option: A

Polarizing angle for water is $53^o4'$. If light is incident at this angle on the surface of water and reflected the angle of refraction is:

polarisation of light polarisation wave optics optics physics

  1. $53^o4'$

  2. $126^o56'$

  3. $36^o56'$

  4. $30^o4'$

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Correct Option: C