Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

The focal length of a thin convex lens for red and blue rays are $100\ cm$ and $96.8\ cm$ respectively. The dispersive power of the material of the lens is

  1. 0.0325

  2. 0.825

  3. 0.968

  4. 0.98
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Dispersive power (omega) for a thin lens is (f_r - f_b) / f_mean. f_mean = (100 + 96.8) / 2 = 98.4. Omega = (100 - 96.8) / 98.4 = 3.2 / 98.4 = 0.0325.

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

Using the following data,choose the correct option:
                     C        D        F      
 Crown   1.5145   1.5170  1.5230   
FLINT    1.6444    1.6520  1.6637                  

  1. The dispersive power for crown glass is 0.1644

  2. The dispersive power for flint glass is 0.029601

  3. The dispersive power for crown is 0.01644

  4. The dispersive power for flint glass is 1.29601
Reveal answer Fill a bubble to check yourself
B,C Correct answer
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,
$w _{1} : w _{2} = [(10-6) * 2 / (10+6)] : [(8-4.5)*2)/ (8+4.5)]$

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