Home
Class 12
PHYSICS
The focal lengths of a convex lens for r...

The focal lengths of a convex lens for red, yellow and violet rays are 100 cm, 98 cm and 96 cm respectively. Find the dispersive power of the material of the lens.

Text Solution

Verified by Experts

The correct Answer is:
A, D
The focal length of lens is given by,
`(1)/(f) = (mu - 1). (1)/(R_1) - (1)/(R_2)`
`rArr (mu - 1) = (1)/(f)xx (1)/((1)/(R_1) - (1)/(R_2))`
`=(k)/(f)….. (i)`
so, `mu_r -1 = (k)/(100) … (ii)`
`mu_y -1 = (k)/(98)…. (ii)`
and `mu_(upsilon) -1 = (k)/(96) ..... (ii)`
So, Dispersive power ` =omega`
`=(mu_(upsilon)j - mu_r)/(mu_y -1)`
`=(mu_(upsilon) -1) - (mu_r -1))/((mu_y -1))`
` =((k)/(96) - (k)/(100))/((k)/(98)) = (98xx 4)/(9600)`
=0.0408
Promotional Banner

Topper's Solved these Questions

  • DISPERSION AND SPECTRA

    HC VERMA|Exercise Objective 2|1 Videos

  • CAPACITORS

    HC VERMA|Exercise Exercise|2 Videos

  • ELECTRIC CURRENT IN CONDUCTORS

    HC VERMA|Exercise Exercises|84 Videos

Similar Questions

Explore conceptually related problems

Focal length of convex lens for red, green and blue colour are f_r , f_g , and f_b respectively, so which of the following statements is true ?

If the focal length of a lens for red and violet light rays respectively are f_R and f_V then which of the following is true relationship ?

A point source of light is kept at a distance of 15cm from a converging lens,on its optical axis.The focal length of the lens is 10cm and its diameter is 3cm ,A screen is placed on the other side of the lens ,perpendicular to the axis of lens,at a distance 20cm from it.Then find the area of the illuminated part of the screen?

A convex lens is immersed in a liquid, whose refractive index is equal to the refractive index of the material of the lens. Then its focal length will

The radii of curvature of both the sides of a convex lens are 15 cm and if the refractive index of the material of the lens is 1.5, then focal length of lens in air is ......... cm.

What is the focal length of lens if the image distance remain same by keeping object at 24 cm and 16 cm from lens ?

In the figure shown L is converging lens of focal length 10 cm and M is a concave mirror of radius of curvature 20 cm . A point object O is placed in front of the lens at a distance 15 cm . AB and CD are optical axes of the lens mirror respectively. Find the coordinates of the final image formed by this system taking O as origin. The distance between CD & AB is 1mm.

What is the focal length of a convex lens of focal length 30cm in contact with a concave lens of focal length 20cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.

A pin is placed 10cm in front of a convex lens of focal length 20cm, made of a material having refractive index 1.5 . The surface of lens farther away from the pin is silvered and has a radius of curvature 22cm. Determine the position of the final image. Is the image real or virtual?