Question

A concave lens of focal length 20cm forms a image 30cm from the lens.how far is the object placed from the lens

Answer 1

Answer:

6 cm

Explanation:

Given,

focal length,f=-–20 cm

image distance,v=–30cm

object distance,u=?

We know,

1/u=1/v–1/f

1/u=1/–30–(1/–20)

1/u=1/–30+1/20

1/u=1/6(by L.C.M.)

u=6

object distance=6cm