Question

# The focal length of a convex lens made of flint glass is 15cm. To remove its chromatic aberration, it is placed in contact with a concave lens made of crown glass. Find the focal length of the concave lens. The ratio of dispersive powers of flint glass to crown glass is 1.5.

A
10cm
B
+10cm
C
20cm
D
+20cm
Solution
Verified by Toppr

#### Given: The focal length of a convex lens made of flint glass is 15cm. To remove its chromatic aberration, it is placed in contact with a concave lens made of crown glass. The ratio of dispersive powers of flint glass to crown glass is 1.5.To find the focal length of the concave lensSolution:Let focal length of the convex lens be f1 and focal length of the concave lens be f2 and ratio of dispersice power of the flint glass is $\dfrac {\omega_2}{\omega_1}=1.5$For achromatic combination,f1f2=−ω2ω1⟹15f2=−1.5⟹f2=−10cmHence the focal length of the concave lens is -10cm

0
Similar Questions
Q1

A convergent lens made of crown glass (refractive index 1.5) has focal length 20cm in air. If it is immersed in a liquid of refractive index 1.60, its focal length will be:

View Solution
Q2

A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a

View Solution
Q3

A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:
(a) +10 cm
(b) +20 cm
(c) −10 cm
(d) −20 cm

View Solution
Q4

An equi-concave lens is to be made of crown glass. What should be radii of the surfaces of the lens if the power of the lens is 2.5 dioptre and refractive index of crown glass is 1.65?

View Solution
Q5

A thin convex lens which is made of glass (refractive index 1.5) has a focal length of 20 cm.it is now completely immersed in a transparent liquid having refractive index 1.75. Find the new focal length of the lens.

View Solution
Solve
Guides