Tag: polarisation of light

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Questions Related to polarisation of light

Multiple choice polarisation of light polarisation wave optics optics physics

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

  1. $33^{\circ}$
  2. $38^{\circ}$
  3. $25^{\circ}$
  4. $43^{\circ}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

So the angle is $90°-57°=33°$

Multiple choice polarisation of light polarisation wave optics optics physics

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

  1. $\lambda\ tan\phi$
  2. $\dfrac{\lambda}{\tan {\phi}}$
  3. $\dfrac{\lambda}{\cos{\phi}}$
  4. $\dfrac{\lambda}{\sin{\phi}}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The wavelength in a medium is lambda_medium = lambda_vacuum / mu. Since mu = tan(phi) at the polarizing angle, lambda_medium = lambda / tan(phi).

Multiple choice polarisation of light polarisation wave optics optics physics

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 ?

  1. $37^{o}$
  2. $53^{o}$
  3. $30^{o}$
  4. $60^{o}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Brewster's angle i_p = tan^-1(mu) = tan^-1(4/3) = 53 degrees. The angle with the horizon is 90 - 53 = 37 degrees.

Multiple choice polarisation of light polarisation wave optics optics physics

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.

  1. $30^{o}$
  2. $45^{o}$
  3. $60^{o}$
  4. $70^{o}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Malus's Law: I = I_0 * cos^2(theta). We want I = I_0/2, so cos^2(theta) = 1/2, which means cos(theta) = 1/sqrt(2), so theta = 45 degrees.

Multiple choice polarisation of light polarisation wave optics optics physics

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:

  1. $30^{0}$
  2. $60^{0}$
  3. $45^{0}$

  4. NONE
Reveal answer Fill a bubble to check yourself
A Correct answer
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] 
$\Rightarrow \theta _B=tan^{-1}\left ( \dfrac{c}{v} \right )=tan^{-1}\left ( \dfrac{3\times 10^{8}}{\sqrt{3}\times 10^{8}} \right )$  
$= tan^{-1}\left ( \dfrac{1}{\sqrt{3}} \right )$ 
$\Rightarrow \theta _{B}=30^{o}$
Multiple choice polarisation of light polarisation wave optics optics physics

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 

  1. $I _0$
  2. $\displaystyle \dfrac{I _0}{2}$
  3. $\dfrac{{{I _o}}}{4}$

  4. Zero
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice polarisation of light polarisation wave optics optics physics

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice polarisation of light polarisation wave optics optics physics

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

  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 $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

sin(theta_c) = 1/mu = sin(45) = 1/sqrt(2), so mu = sqrt(2) = 1.414. Polarizing angle i_p = tan^-1(1.414) = 54.7 degrees. Angle of refraction r = 90 - 54.7 = 35.3 degrees.

Multiple choice polarisation of light polarisation wave optics optics physics

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.

  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 $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Given i_p = 53 degrees. Angle of refraction r = 90 - 53 = 37 degrees. Refractive index mu = tan(53) = 1.327.

Multiple choice polarisation of light polarisation wave optics optics physics

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

  1. 3:4

  2. 4:3
  3. $\sqrt { 3 } : 2$
  4. $2 : \sqrt { 3 }$
Reveal answer Fill a bubble to check yourself
A Correct answer
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.