A converging lens of focal length 5cm forms a virtual image which is 20cm from the lens. How far from the lens is the object?

adewumi2005

5 years ago

Since it's a convex lens but the image is virtual therefore v=-20cm
f=5cm, 1/f=1/u-1/v
1/5+1/20=1/u
5/20=1/u
1/4=1/u
U=4cm(ans)

kemiluv2024

1 year ago

To solve this problem, we can use the lens equation:

1/f = 1/do + 1/di

where:
f = focal length = 5cm
di = distance to image = -20cm (virtual image, so it's negative)
do = distance to object (which we want to find)

Rearranging the equation to solve for do, we get:

1/do = 1/f - 1/di
= 1/5 - 1/-20
= 1/5 + 1/20
= 4/20 + 1/20
= 5/20
= 1/4

So, do = 4cm

The correct answer is B. 4.0 cm.