Tag: wave optics

Quizzes (12) Questions (312)

Questions Related to wave optics

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.
Multiple choice polarisation of light polarisation wave optics optics physics

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.

  1. (A) and (D) are true

  2. (A) and (B) are true

  3. (A) and (C) are true

  4. (B) and (C) are true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

At Brewster's angle, the reflected and refracted rays are perpendicular (A). The reflected light is polarized perpendicular to the plane of incidence (C is incorrect). The refracted light is partially polarized (D is correct).

Multiple choice polarisation of light polarisation wave optics optics physics

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

  1. $I _{0}$
  2. $I _{0}/2$
  3. $I _{0}/4$
  4. $I _{0}/8$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When unpolarized light of intensity I0 passes through the first polaroid A, its intensity becomes I1 = I0 / 2. When it passes through the second polaroid B at an angle of 45 degrees, Malus's law applies: I2 = I1 * cos^2(45) = (I0 / 2) * (1 / 2) = I0 / 4.

Multiple choice polarisation of light polarisation wave optics optics physics

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:

  1. $53^o4'$
  2. $126^o56'$
  3. $36^o56'$
  4. $30^o4'$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

At the polarizing angle, i_p + r = 90 degrees. r = 90 - 53 degrees 4 minutes = 36 degrees 56 minutes.