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 perceive colours resolution of optical instruments lenses option c: imaging physics

The angles of minimum deviations are 53$^{\circ}$ and 51$^{\circ}$ for blue and red colors respectively produced in an equilateral glass prism. The dispersive power is :

  1. $\dfrac{2}{51}$
  2. $\dfrac{1}{26}$
  3. $\dfrac{1}{52}$
  4. $\dfrac{1}{51}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As $\delta _{Y}=\dfrac{\delta _{B}+\delta _{R}}{2}$


So $\delta _{Y}=\dfrac{53^{\circ }+51^{\circ }}{2}$ =52$^{\circ }$

$\therefore dispersive\ power\ =\dfrac{\delta _{B}-\delta _{R}}{\delta _{Y}}$

                                    $=\dfrac{53-51}{52}$

                                    $=\dfrac{2}{52}$

                                    $=\dfrac{1}{26}$

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

If the refractive indices of crown glass for red, yellow and violet colours are respectively ${ \mu  } _{ r },{ \mu  } _{ y },{ \mu  } _{ v }$, then the dispersive power of this glass would be

  1. $\cfrac { { \mu } _{ v }-{ \mu } _{ r } }{ { \mu } _{ y }-1 } $
  2. $\cfrac { { \mu } _{ v }-{ \mu } _{ y } }{ { \mu } _{ r }-1 } $
  3. $\cfrac { { \mu } _{ v }-{ \mu } _{ y } }{ { \mu } _{ y }-{ \mu } _{ r } } $
  4. $\cfrac { { \mu } _{ v }-{ \mu } _{ r } }{ { \mu } _{ y } } -1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Dispersive power of a glass is given by ratio of difference of reflective index of two extreme wavelength to the difference of intermediate wavelength to unity i.e.


$ { Dispersive\quad Power\quad =\quad \dfrac { { \mu  } _{ v }-{ \mu  } _{ r } }{ { \mu  } _{ y }-1 }  } $

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

In a prism, the refractive indices of different colours are
$\mu _{V} =$ 1.6;
$\mu _{R} =$ 1.52;
$\mu _{Y} =$ 1.56.
The dispersive power of the prism is :

  1. $\dfrac{1}{56}$
  2. $\dfrac{1}{8}$
  3. $\dfrac{1}{7}$

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

Dispersive power of prism= $w=\dfrac{\mu _{V}-\mu _{R}}{\mu _{Y}-1}$


$w=\dfrac{1.6-1.52}{1.56-1}$

$w=\dfrac{1}{7}$

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

A flint glass prism is of refracting angle 5$^{\circ}$. Its refractive index for C line is 1.790 and for F line is 1.805. The angular dispersion of C and F lines is:

  1. 0.075$^{\circ}$
  2. 0.085$^{\circ}$
  3. 0.095$^{\circ}$
  4. 0.065$^{\circ}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Deviation for C line $= \text{(Refractive index for C line -1) x Refracting angle}$

                                 $= (1.79-1) \times 5$
                                 $=3.95^o$

Deviation for F line $= \text{(Refractive index for F line -1) x Refracting angle}$

                                 $= (1.805-1) \times 5$      
                                 $= 4.025^o$

So the angular dispersion of C and F line is the deviation difference between F and C line.
Angular dispersion $= 4.025 -3.95 = 0.075^o$

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

Dispersive power of the material of a prism is 0.0221. If the deviation produced by it for yellow colour is 38$^{\circ}$, then the angular dispersion between red and violet colours is :

  1. 0.65$^{\circ}$
  2. 0.84$^{\circ}$
  3. 0.48$^{\circ}$
  4. 1.26$^{\circ}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As Dispersive power $ = \dfrac{Angular  \  dispersion}{mean  \ deviation}$


We take the deviation for yellow color as the mean deviation

$\Longrightarrow$  $\omega=\dfrac{\delta _{V}-\delta _{R}}{\delta _{Y}}$


$\Longrightarrow$  $0.0221=\dfrac{\delta _{V}-\delta _{R}}{38^{\circ }}$

$\Longrightarrow$  $\delta _{\nu}-\delta _{R}=0.84^{\circ }$

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

If a glass prism is dipped in water, its dispersive power

  1. increases

  2. decreases

  3. does not change
  4. may increase or decrease depending on whether the angle of the prism is less than or greater than $60^o$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Dispersive power of a prism $=\dfrac{\mu _{v}-\mu _{r}}{\mu-1}$


Here the refractive indices are with respect to the medium in which prism is kept.

Hence when in water, dispersive power $=\dfrac{\dfrac{\mu _{v}}{\mu _{water}}-\dfrac{\mu _{r}}{\mu _{water}}}{\dfrac{\mu}{\mu _{water}}-1}$
$=\dfrac{\mu _{v}-\mu _{r}}{\mu-\mu _{water}}$

Hence dispersive power increases when prism is dipped in water.

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

Two thin prisms of flint glass, with refracting angles of $6^o$ and $8^o$ respectively, possess disperse powers in the ratio 

  1. 4 : 3

  2. 3 : 4

  3. 1 : 1

  4. 9 : 16
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Dispersive power = $\dfrac{\mu _v-\mu _r}{\mu-1}$ 

Since, it does not depend on angle of prism, dispersive power f both prism will be same.
Therefore, C is correct option.

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

Refractive index of glass for red and violet colours are $1.64$ and $1.66$ respectively. Dispersive power of the prism is :

  1. $0.3$
  2. $3.3$
  3. $1.33$
  4. $.03$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Dispersive power (omega) = (mu_v - mu_r) / (mu_mean - 1). Assuming mu_mean = (1.64 + 1.66) / 2 = 1.65. Omega = (1.66 - 1.64) / (1.65 - 1) = 0.02 / 0.65 = 0.0307, which rounds to 0.03.

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

The refractive index of flint glass for blue line is 1.6333 and red line is 1.6161, then dispersive power of the glass is :

  1. 0.0276

  2. 0.276

  3. 2.76

  4. 0.106
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given :     $n _b = 1.6333$             $n _r = 1.6161$

Refractive index for yellow light    $n _y = \dfrac{n _b+n _y}{2}$
$\therefore \ n _y = \dfrac{1.6333+1.6161}{2} = 1.6247$
Dispersive power     $w = \dfrac{n _b-n _r}{n _y - 1} = \dfrac{1.6333-1.6161}{1.6247-1} = 0.0276$

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

If D is the deviation of a normally falling light beam on a thin prism of angle a and $\delta$ is the dispersive power of the same prism then

  1. D is independent of A

  2. D is independent of refractive Index
  3. $\delta$ is independent of refractive index
  4. $\delta$ is independent of A
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using relation $ D=\left( { \mu  } _{ v }-{ \mu  } _{ r } \right) A$


and $ \delta =\dfrac { { \mu  } _{ v }-{ \mu  } _{ r } }{ { \mu  } _{ y }-1 } $ we get,

$ \delta$ is independent of $A$

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

If a glass prism is dipped in water, its dispersive power

  1. increases

  2. decreases

  3. does not change
  4. may increase or decreases depending on whether the angle of the prism is less than or greater than $ { 60 }^{ \circ }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Glass prism works on the principle that lights with different colours travels with different speed in solid and liquid medium. So when a glass prism is dipped in water the light that reaches it is already some what dispersed by water, and the prism does still more. Hence its dispersive power decreases.

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

A thin prism deviates blue and red rays through 10$^{\circ}$ and 6$^{\circ}$respectively. Another prism deviates same colours through 8$^{\circ}$ and 4.5$^{\circ}$ respectively.The ratio of dispersive powers of the prisms is :

  1. 5:4

  2. 4:5

  3. 25:28

  4. 5:28
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

For a thin prism,

Dispersive power, $w = (\delta _{v}-\delta _{r}) / \delta _{y}$

Also, $\delta _{y} = (\delta _{v}+\delta _{r})/2$

Ratio of dispersive power,
$w _{1} : w _{2} = [(10-6) * 2 / (10+6)] : [(8-4.5)*2)/ (8+4.5)]$

=> $w _{1} : w _{2} = 25:28$

Multiple choice perceive colours resolution of optical instruments lenses option c: imaging physics

A prism of a certain angle deviates the red and blue rays by $8$ and $12$ respectively. Another prism of the same angle deviates the red and blue rays by $10$ and $14$ respectively. The prisms are small angled and made of different materials. The dispersive powers of the materials of the prisms are in the ratio

  1. $11 : 9$
  2. $6 : 5$
  3. $9 : 11$
  4. $5 : 6$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Dispersive power $= \cfrac{\mu _v - \mu _r}{\mu _y -1} = \cfrac{\delta _v + \delta _r}{\delta _y}$

$\delta _y = \cfrac{\delta _v + \delta _r}{2}$

The ratio of dispersive power is;
$\cfrac{12-8}{\cfrac{12+8}{2}}$= $\cfrac{\cfrac{4}{10}}{\cfrac{4}{12}}$ =$ \cfrac{12}{10} $= $ 6 : 5 $