Question

Choose the correct answer from given options
A biconvex lens of focal length f is cut into two identical plano-convex lenses. The focal length of each part will be

विकल्प

• f

• f/2

• 2f

• 4f

Answer 1

Let the focal of the equiconvex lens be f and that of the plano-convex lens be f'.
Let the radius of curvature for the equiconvex lens be R.
Applying Lens maker's formula 

`1/f = (mu - 1)(1/R + 1/R) = (2(mu - 1))/R`

For the plano-convex lens, the focal length can be calculated as:

`1/f' = (mu - 1)(1/R) = (mu - 1)/R`

Thus, f' = 2f
Thus, the focal length of the plano-convex lens is twice that of the equiconvex lens.

Hence, the correct answer is option 2f.