Question

A convex lens of refractive index \[ \frac{3}{2} \] has a power of \[ 5\,D. \] If it is placed in a liquid of refractive index \(2\), the new power of the lens is

• A. \(2.5\,D\)
• B. \(1.25\,D\)
• C. \(-1.25\,D\)
• D. \(-2.5\,D\)

Hint:

For a lens immersed in a medium, \[ P_{\text{medium}} = \frac{\left(\frac{n_l}{n_m}-1\right)} {(n_l-1)} \,P_{\text{air}}. \] If the medium has a higher refractive index than the lens, the power becomes negative and a convex lens behaves like a concave lens.

Answer 1

The Correct Option is D