Question

A thin, symmetric double­convex lens of power P is cut into three parts A, B and C as shown. The power of

(1)  A in P

(2)  A in 2p

(3) B is P/2

(4)  B is P/4

Answer 1

Correct option (3) B is P/2

Explanation :

When cut along horizontal, R₁ and R₂ 

Are as it is, so P_er = P

When cut along vertical, 

R₁ → R₁,R₂ → ∞

So, f'  → 2f Hence P  → P/2