Question

A convex lens forms an image of an object placed 20cm away from it at a distance of 20cm on the other side of the lens. If the object is moves 5cm toward the lens, the image will be
A. `5 cm` towards the lens
B. `5 cm` away from the lens
C. `10 cm` towards the lens
D. `10 cm` away from the lens

Answer 1

Correct Answer - D
Clearly, `2f=20cm`
or `=10cm`
Now, `u=-15cm, v=?`
`f=10cm`
`(1)/(v)-(1)/(-15)=(1)/(10)`
or `(1)/(v)+(1)/(15)=(1)/(10)` or `(1)/(v)=(1)/(10)-(1)/(15)`.
or `(1)/(v)=(3-2)/(30)=(1)/(30)`
or `v=30cm`
The change in image distance is `(30-20)` i.e., `10 cm`.