Question

An object places at 30cm from a converging lens forms a real image at a distance of 15cm from the lens find​

Answer 1

To find the focal length

u = -30

v = 15 cm

Formula to find focal length

1/v  -   1/u = 1/f

Applying the formula we get

1/15 -1/30 =1/f

1/30 = 1/f

f = 30cm

$\boxed{Focal length = 30cm}$

Answer 2

or

here

U. = -30

V. = +15

F. = ?

using lens formula , we get:

1/v - 1/u =1/f

1/15 - (1/-30) =1/f

1/15 + 1/30 =1/f

2+1/30 =1/f

1/f = 3/30

1/f =1/10

f = 10

focal length is 10 cm