Physics · Science General

Optics and Light Properties

2,019 Questions

Optics and light properties focus on the behavior of light, including reflection, refraction, dispersion, and polarization. This topic also covers the wave nature of light, illumination, and the functioning of optical instruments like microscopes. Questions on these concepts are common in general science sections of SSC, Railways, and State exams.

Reflection and mirrorsRefraction and mediumsLight wave theoriesPolarization and intensity

Optics and Light Properties Questions

Multiple choice polarisation of light polarisation wave optics optics physics

ASSERTION (A):Hyugens' theory failed to explain polarization
REASON (R): According to Hyugens' theory light is longitudinal wave

  1. A is correct, R is correct and it is the correct explanation

  2. A is correct, R is correct but it is not a correct explanation

  3. A is correct, R is wrong

  4. A is wrong , R is correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Huygen's theory failed to explain polarisation because according to the Huygen's theory light is a longitudinal waves and longitudinal wave does not shows polarisation.

Multiple choice polarisation of light polarisation wave optics optics physics

According to Maxwell , most of the optical properties of light depend on

  1. Magnetic vector

  2. Electric vector

  3. Both Electric and Magnetic vectors

  4. Can not be decided
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The experiments on stationary light waves establish that most of the optical properties of light depends on the electric vector, which is also known as light vector.

Multiple choice polarisation of light polarisation wave optics optics physics

Identify which of the following should be used for polarised light waves?
I. Sunglasses
II. Remove ultraviolet light
III. Reveal stress patterns

  1. I only

  2. II only

  3. I and III only

  4. II and III only

  5. I, II, and III
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Polarizers are used in industry to reveal stress patterns in machinery and tools. Sunglasses are used to protect the eyes by polarizing the light to reduce glare using the tailor-made material of the glasses.

Multiple choice polarisation of light polarisation wave optics optics physics
Three waves are given below.
I. Sound waves
II. Visible light waves
III. X-rays

Which of the above waves cannot be polarised?

  1. I only

  2. III only

  3. I and II only

  4. I and III only

  5. I, II and III
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Only the transverse waves can be polarized.

As the sound waves are longitudinal waves in nature whereas visible light rays and X-rays are transverse waves.
Thus sound waves cannot be polarized.

Multiple choice polarisation of light polarisation wave optics optics physics

Light waves exhibit polarization but sound waves do not exhibit polarization because they are not:

  1. longitudinal

  2. coherent

  3. dispersive

  4. transverse

  5. refractive
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Only transverse waves can exhibit polarization.
Light waves are transverse waves whereas sound waves are longitudinal waves, hence sound waves can not be polarized.

Multiple choice polarisation of light polarisation wave optics optics physics

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

  1. refraction.

  2. reflection

  3. Interference

  4. diffraction

  5. polarization.
Reveal answer Fill a bubble to check yourself
E Correct answer
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.

Multiple choice polarisation of light polarisation wave optics optics physics

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

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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 .

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
A 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.