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 conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

Light starting from a medium of refractive
index $  \mu  $ undergoes refraction into a medium of index $  \mu  $. If I and r stand for angle of incidence are refraction respectively :

  1. $

    \frac{\sin i}{\sin r}=\frac{\mu}{\mu^{\prime}}

    $
  2. $

    \frac{\sin i}{\sin r}=\frac{\mu^{\prime}}{\mu}

    $
  3. $

    \frac{\cos i}{\cos r}=\frac{\mu^{\prime}}{\mu}

    $
  4. $

    \frac{\sin i}{\sin r}=1 / \mu \mu^{\prime}

    $
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

When a light ray is refracted from one medium into another the wavelength change from $4500{ A }^{ 0 }$ to $3000{ A }^{ 0 }$ the critial angle for a ray from second medium to first medium is 

  1. ${ sin }^{ -1 }\left( \dfrac { 2 }{ 3 } \right) $
  2. ${ cos }^{ -1 }\left( \dfrac { 2 }{ 3 } \right) $
  3. ${ tan }^{ -1 }\left( \dfrac { 3 }{ 2 } \right) $
  4. ${ tan }^{ -1 }\left( \dfrac { 2 }{ \sqrt { 5 } } \right) $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Refractive index mu = lambda1 / lambda2 = 4500 / 3000 = 1.5 = 3/2. The critical angle C is given by sin(C) = 1 / mu = 1 / 1.5 = 2/3. Thus, C = sin^-1(2/3).

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

A wave has velocity $u$ in medium $P$ and velocity $2u$ in medium $Q$. If the wave is incident in medium $P$ at an angle of $30^\circ$ then the angle of refraction will be

  1. $30^\circ$
  2. $45^\circ$
  3. $60^\circ$
  4. $90^\circ$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using Snell's Law: sin(i) / sin(r) = v1 / v2. Given i = 30 degrees, v1 = u, v2 = 2u. sin(30) / sin(r) = u / 2u = 1/2. sin(r) = 2 * sin(30) = 2 * 0.5 = 1. Therefore, r = 90 degrees.

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

What is the angle of incidence if a ray of light is not deviated when it enters a block of glass?

  1. $30^{\circ}$
  2. $60^{\circ}$
  3. $90^{\circ}$
  4. $0^{\circ}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The angle of incidence if a ray of light is not deviated when it enters a block of glass :

The angle of incidence is equal to angle of refraction only if the angle the  deviation is zero. This is practically impossible since, when light enters a medium from another medium it has to undergo refraction. So angle of minimum deviation is never zero but it can be a very small value. And angle of incidence is never equal to angle of refraction, if the light undergoes minimum deviation. But the angle of incidence is equal to the angle of emergence.

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

An under water swimmer looks upward at an unobstructed overcast sky. The vertex angle does the sky appear to subtend at the eye of swimmer is (critical angle for water air interface is  $C$).

  1. $C$
  2. $C/2$
  3. $2 C$
  4. $3 C$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A swimmer looking up sees the sky through a cone of light defined by the critical angle C. The total angle subtended at the eye is 2 * C.

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

When a ray of light strikes the glass slab at $90^{\circ}$, it is seen that it does not deviate from its path. In such a situation :

  1. angle of incidence is zero

  2. angle of refraction is zero

  3. both(a) and (b)

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 If the rays of light are incident upon the glass surface perpendicularly, or at 90 degree angle to the surface, the rays will pass through without changing direction. In this case, the angle of incidence and angle of refraction are always zero.
Hence, the option A and B are correct.

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

The velocity of light in air is $3\times 10^{10} cm/\sec$. If the refractive index of glass with respect to air is $1.5$, then velocity of light in glass is

  1. $2\times 10^{10} cm/\sec$
  2. $4.5\times 10^{10} cm/\sec$
  3. $3\times 10^{10} cm/\sec$
  4. $1\times 10^{10} cm/\sec$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The refractive index mu = c / v_glass. Given mu = 1.5 and c = 3 * 10^10 cm/s, v_glass = c / mu = 3 * 10^10 / 1.5 = 2 * 10^10 cm/s.

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

A bird in air looks at a fish vertically elow it and inside water. X is the height of the bird above the surface of water and Y the depth of the fish below the surface of water if refractive index of water with respect to air is $ \mu $. The distance of the fish as observed by the bird is 

  1. X + Y
  2. $ X + Y/ \mu $
  3. $ \mu X + Y $
  4. $ \mu X + \mu Y $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The bird sees the fish at an apparent depth. The fish is at depth Y, which appears at Y' = Y / (1/mu) = mu * Y. The bird is at height X. The total distance observed by the bird is X + mu * Y.

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

A ray of light passes from a medium L to a medium K. No refraction of light occurs if the ray of light hits the boundary of these two media at the angle of incidence equal to ...............

  1. $30^{\circ}$
  2. $90^{\circ}$
  3. $0^{\circ}$
  4. $120^{\circ}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If a light is an incident at an angle of $90^{o}$ it will go straight again making an angle of $90^{o}$ with the normal it doesn't depend on medium.
so the angle of incidence is $90^{o}$
A because if an angle of incidence is 90°, it means the light is propagating along the interface separating the two media. In this case, the light does not enter the second medium and so we can not talk about the angle of refraction. The angle of refraction can also be regarded as 90°.

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

The critical angle for refraction from medium -1 to air is ${ \theta  } _{ 1 }$ and that from medium -2 to air is ${ \theta  } _{ 2 }$. If medium -2 is denser then medium -1. Find the critical angle for refraction from medium -2 to medium. 

  1. ${ sin }^{ -1 }(\frac { { sin\theta } _{ 2 } }{ { sin\theta } _{ 1 } } )$
  2. ${ sin }^{ -1 }(\frac { { sin\theta } _{ 1 } }{ { sin\theta } _{ 2 } } )$

  3. Both A and B

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

From medium 1 to air


$\eta _1sin\theta _1 = \eta _2sin\theta _2$

 here $\eta _2$ = 1 (air)

$\eta _1 = \frac{1}{sin\theta _1}$

Similarly for medium 2 to air

$\eta _2 = \frac{1}{sin\theta _2}$

Now from medium (2) to (1)

$\eta _2sin\theta _2 = \eta _1sin\theta _2$

$sin\theta _c = \frac{sin\theta _2}{sin\theta _1}$

$\theta _c = sin^{-1}(\frac{sin\theta _2}{sin\theta _1})$

Multiple choice conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

If any two media are optically exactly the same then; when light passes from one medium to another then:

  1. No bending occurs

  2. Sometimes it can bend

  3. Compete bending occurs

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since, both media are optically same, there is no difference in the absolute refractive indices of the two media.

        Hence, light passes through them undeviated that is no bending occurs.

Answer-(A)