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An object is placed at a distance of 40 ...

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

A

30 cm towards the mirror

B

36 cm away from the mirror

C

30 cm away from the mirror

D

36 cm towards from the mirror .

Text Solution

Verified by Experts

The correct Answer is:
B

`(1)/(f)=(1)/(v_(1))+(1)/(u)`
`-(1)/(15)=(1)/(v_(1))-(1)/(40)`
`implies (1)/(v_(1))=(1)/(-15)+(1)/(40)`
`v_(1)` =-24 cm
When object is displaced by 20 cm towards mirror
`u_(2)=-20`
`(1)/(f)=(1)/(v_(2))+(1)/(u_(2))`
`(1)/(-15)=(1)/(v_(2))-(1)/(20)`
`(1)/(v_(2))=(1)/(20)-(1)/(15)`
So, image shifts away from mirror by `=60-24=36 cm`
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