The figure shows and equiconvex lens of focal length f. It the lens is cut along PQ, the focal length of each half will be

Options

A. `f/2`
B. f
C. 2f
D. 4f

Answer

C

Explanation

(c ) According to lens maker's formula,
`1/f=(mu-1)(1/R-1/((-R)))`
`rArr1/f=(mu-1)(2/R)`
On cutting , `1/f'=(mu-1)1/R-1/oo`
`1/f'=(mu-1)(1/R)`
From Eqs. (i) and (ii), we get f'=2f