An object is placed at a distance of `40 cm` from a concave mirrorr of focal length `15 cm`. If the object is displaced through a distance of `20 cm` towards the mirrorr, the displacement of the image will be

Options

A. 30 cm towards the mirror
B. 30 cm away from the mirror
C. 30 cm away from the mirror
D. 36 cm towards the mirror

Answer

B

Explanation

`(1)/(f)=(1)/(v)+(1)/(u)`
`-(1)/(15)=(1)/(v_(1))-(1)/(40)`
`rArr" "(1)/(v)=(1)/(-15)+(1)/(40)`
`v_(1)=-24cm`
When object is displaced by 20 cm towards the mirror then object distance becomes 20 cm from mirror.
`(1)/(f)=(1)/(v)+(1)/(u)`
`(1)/(-15)=(1)/(v)-(1)/(20)`
`(1)/(v)=(1)/(20)-(1)/(15)`
`v=-60cm`
So, image moves away from the mirror by a distance `60 - 24 = 36 cm`.
Hence option (b) is correct.