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
Medium
Open in App
Updated on : 2022-09-05
Solution
Verified by Toppr
Correct option is A)
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 lens
Solution:
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,
f2f1=−ω1ω2⟹f215=−1.5⟹f2=−10cm
Hence the focal length of the concave lens is -10cm
Solve any question of Ray Optics and Optical Instrument with:-