If the bio-convex lens is cut as shown in the figure, the new focal length f' is

Options

A. 2f
B. f
C. `(f)/(2)
D. Infinite

Answer

A

Explanation

`f=(mu-1)((1)/(R_(1))-(1)/(R_(2)))`
`f=(mu-1)((1)/(R)+(1)/(R))`
`f=(mu-1)(2)/(R)" "......(i)`
and `f,=(mu-1)((1)/(R)-(1)/(oo))`
`f.=((mu-1))/(R)" "......(ii)`
From equations (i) and (ii), we get
f.=2f