A convex lens of focal length 15 cm is placed on a plane mirror. An object is placed 20 cm from the lens. The image is formed

Options

A. 12 cm in front of the mirror
B. 60 cm behind the mirror
C. 60 cm in front of the mirror
D. 30 cm in front of the mirror

Answer

A

Explanation

Equivalent focal length
`(1)/(F)=(1)/(f_l)+(1)/(f_m)+(1)/(f_l)`
`=(2)/f_(l)_(1)/(f_m)=(2)/(15)+(1)/(infty)`
`F=15//2cm`
This combination will behave as concave as concave mirror of focal length 7.5 cm
`(1)/(v)+(1)/(u)=(1)/(f)`
`(1)/(v)+(1)/(-20)=(1)/(-7.5)`
`(1)/(v)=-(2)/(15)+(1)/(20)=(-8+3)/(60)impliesv=-12cm`