Question

If an object is placed at a distance of 30 cm and the image is formed at a distance of 10 cm on the same side of the lens, then find the focal length of the lens used.
please explain with sign convention.​

Answer 1

u = -30. v=10. f=?

1/f=1/v-1/u

Answer 2

Given

U= -30cm

V=-10cm

By lens formula

1/f =1/v-1/u

i.e. 1/f = -1/10 - (-1/30)

= -1/15

i.e. f= -15 cm

The lens used is concave lens

Image formed between pole and focal length

I didn't show the calculation but hope this helps

All the best for upcoming exam