When an object is placed 40cm from a diverging lens, its virtual image is formed 20cm from the lens. The focal length and power of lens are

Options

A.
B.
C.
D.

Answer

C

Explanation

We have, `(1)/(f)=(1)/(v)-(1)/(u) Rightarrow (1)/(f)=(1)/(-20)-(-(1)/(40))`
`=(-2+1)/(40)=-(1)/(40)`
or f=-40cm
Power of lens, `P=(200)/(0.40)=-2.5D`