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

A plane polarized light passed through successive polarizers which are rotated by $30^{\circ}$ with respect to each other in the clockwise direction. Neglecting absorption by the polarizers and given that the first polarizer's axis is parallel to the plane of polarization of the incident light, the intensity of light at the exit of the fifth polarizer is closest to.

  1. Same as that of the incident light
  2. $17.5$% of the incident light
  3. $30$% of the incident light

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

$I=I _o (cos^2\phi)^4$

$I=I _o (cos^230)^4$
$I=30$% of $I _o$

Multiple choice polarisation of light polarisation wave optics optics physics

The refractive index of the medium, for the polarising angle $60^o$ is?

  1. $1.732$
  2. $1.414$
  3. $1.5$
  4. $1.468$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Relation between refractive index of medium and polarising angle is given by
$n = \tan i _p$
Given :  Polarising angle  $i _p = 60^o$
So, refractive inedx  $n = \tan (60^o) = 1.732$

Multiple choice polarisation of light polarisation wave optics optics physics

A beam of natural light falls on a system of 5 polaroids, which are arranged in succession such that the pass axis of each Polaroid is turned through $60^0$ with respect to the preceding one. The fraction of the incident light intensity that passes through the system is

  1. $\dfrac{1}{64}$
  2. $\dfrac{1}{32}$
  3. $\dfrac{1}{256}$
  4. $\dfrac{1}{128}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice polarisation of light polarisation wave optics optics physics

What proves that light is a transverse wave?

  1. Polarization

  2. Reflection

  3. Refraction

  4. Interference
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A transverse wave is a wave that oscillates perpendicular to its direction of propagation.  Polarization of light proved that light is a transverse wave.

Multiple choice polarisation of light polarisation wave optics optics physics

In the light emerging from calcite crystal :

  1. Both O-ray and E-ray are partially polarised

  2. Both O-ray and E-ray are completely polarised

  3. O-ray is partially polarised and E-ray is completely polarised.

  4. O-ray is completely polarised and E-ray is partially polarised.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Because of birefringence the ordinary and extra ordinary ray are completely polarized.

Multiple choice polarisation of light polarisation wave optics optics physics

In double refraction :

  1. the velocity of the E-ray varies with direction

  2. e-ray does not obey Snell's law
  3. $\mu $ of E-ray is constant

  4. both A and B
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Because the speed of light waves in a medium is equal to their speed in a vacuum divided by the index of refraction for that wavelength, an extra ordinary ray can be either faster or slower than an ordinary ray. The extra ordinary ray does not obey snell's law. It is because refractive index of the e-ray varies according to the direction taken because it has components that are both parallel and perpendicular to the crystal's optic axis.

Multiple choice polarisation of light polarisation wave optics optics physics

In double refraction, the stationary image can be produced by :

  1. O-ray

  2. E-ray

  3. Both O-ray and E-ray combined together

  4. Some times O-ray and some times E-ray
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Only for the ordinary ray the refractive index is observed to be constant in all directions

Multiple choice polarisation of light polarisation wave optics optics physics

When unpolarised light passes through a Polaroid sheet the beam that emerges from it is plane polarized. This is due to selective :

  1. absorption of the O-Ray

  2. absorption of the E-Ray

  3. absorption of the E & O Rays

  4. reflection of one of the rays
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

polaroid has absorption of O- Ray as the phenomenon behind its polarising ability.

Multiple choice polarisation of light polarisation wave optics optics physics

Consider the following statements A & B. Identify the correct choice in the given answers.
(A) The refractive Index of the extra-ordinary ray depends on the angle of incidence in double refraction
(B) The vibrations of light waves acquire onesidedness for both ordinary and extraordinary rays in double refraction

  1. A & B are wrong

  2. A & B are correct

  3. A is correct B is wrong

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

In double - refraction the refractive index of the extra - ordinary ray varies according to the direction taken because it has components that  are both parallel and perpendicular to the crystal's optic axis. Thus (A) is correct.
The ordinary ray and the extraordinary ray are polarized in planes vibrating at right angles to each other. Thus (B) is correct.

Multiple choice polarisation of light polarisation wave optics optics physics

If $\mu _{O}$ and  $\mu _{e}$ are the refractive indices of a double
refracting crystal, then
1)  $\mu _{O}$ < $\mu _{e}$ for quartz crystal
2)  ,$\mu _{O}$ > $\mu _{e}$ for calacite crystal

  1. both 1 and 2 are true

  2. 1 is true 2 is false

  3. 1 false 2 is true

  4. both 1 and 2 are false
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For quartz crystal $\mu _{0}=1.544  ;  \mu _{e}=1.553$
For calacite crystal $\mu _{0}=1.658  ;  \mu _{e}=1.486$
Thus both a and b are true.

Multiple choice polarisation of light polarisation wave optics optics physics

Huygens wave theory could not explain

  1. reflection of light

  2. refraction of light

  3. interference of light

  4. double refraction
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Huygens waves theory could well explain reflection, refraction and interference of light but could not explain the double refraction because in huygens principle light is considered as mechanical wave which could not explain the double refraction.

Multiple choice polarisation of light polarisation wave optics optics physics

The tourmaline crystal

  1. Absorbs ordinary light and transmits extra ordinary

  2. Absorbs extra ordinary light and transmits ordinary light

  3. Both absorbs ordinary and extra ordinary light

  4. Both transmits ordinary light and extra ordinary light
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Some transparent crystals, such as tourmaline and calcite, have the property that when one views an object through them one sees two images of the object. If one passes a narrow beam of light through them, the refracted beam is split into two parts which travel through the crystal and emerge as two separate beams. One of the beams obeys the ordinary laws of refraction and is called the ordinary ray. The other beam is called the extraordinary ray. The extraordinary ray does not always lie in the plane of incidence. Its speed, and consequently its index of refraction, depends on its direction of propagation through the crystal.

Since the speed of the emerging rays and angle are different, the emergent rays are circularly or optically polarized.
Hence both ordinary and extraordinary light are transmitted.
The correct answer is option D.

Multiple choice polarisation of light polarisation wave optics optics physics

What happens to electric field component when unpolarized light is incident on surface such that reflected and refracted light are at right angles?

  1. Parallel component remains in reflected light

  2. Prependicular component remains in reflected
    light

  3. It will remain unpolarized

  4. Partially polarised reflected light.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When unpolarized light is incident at Brewster's angle, the reflected light is plane-polarized. The electric field component perpendicular to the plane of incidence remains in the reflected light, while the parallel component is refracted.

Multiple choice polarisation of light polarisation wave optics optics physics

Two nicol prisms A and B are placed in the path of a beam of unpolarised light, so that no light emerges out of B. In between these two, a third nicol C is placed such that its principal section is at an angle of $30^0$ with that of A. The percentage of intensity of incident unpolarised light that emerges from B.

  1. $2.8$
  2. $9.4$
  3. $15.3$
  4. $10.2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice polarisation of light polarisation wave optics optics physics

Two polaroids are placed in the path of unpolarized beam of intensity ${I _0}$ such that no light is emitted from the secong polaroid. If a third polaroid whose polarization axis makes an angle $\theta $ with the polarization axis of first polaroid, is placed between these polaroids then the intensity of light emerging from the last polaroid will be

  1. $\left( {\frac{{{I _0}}}{8}} \right){\sin ^2}2\theta $
  2. $\left( {\frac{{{I _0}}}{4}} \right){\sin ^2}2\theta $
  3. $\left( {\frac{{{I _0}}}{2}} \right){\sin ^2}2\theta $
  4. ${I _0}{\cos ^4}2\theta $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The first polarizer reduces intensity to I0/2. The second polarizer is at angle theta to the first, so intensity becomes (I0/2) * cos^2(theta). The third polarizer is at 90 degrees to the first, meaning it is at (90-theta) to the second. Intensity = (I0/2) * cos^2(theta) * cos^2(90-theta) = (I0/2) * cos^2(theta) * sin^2(theta) = (I0/2) * (sin(2*theta)/2)^2 = (I0/8) * sin^2(2*theta).