Question

A double convex lens has a focal length of 0.5m in air . Find the focal length of the same lens when immersed in water. the absolute refractive index of glass and water are 1.5 and 1.33 respectively. ​

Answer 1

Answer:

For glass lens in air,.aμg=1.5 and fa=0.2 m

1/fa=(.aμg)(1/R1−1/R2)

10.2=(1.5−1)(1/R1−1/R2)

∴1/R1−1/R2=10

For the same lens in water,

1/fw=(.a/μg.a/μw−1)(1/R1−1/R2)

=(1.51/1.33−1)×10

fw=1.33/1.71=0.78 m

Change in focal length =fw−fa=0.78−0.20

=0.58 m.

Explanation: