Question

a concave lens of focal length 15 cm forms an image 10 cm from the lens. how far is the object placed from the lens?​

Answer 1

Answer:

object is placed at 2f

Explanation:

f = -15 ( concave lens)

v = - 10 ( concave lens)

u = ?

1/f = 1/v - 1/u

1/-15 = 1/-10 - 1/u

-1/15 = -1/10 - 1/u

-1/15 + 1/10 = -1/u

[(-2)+ 3]/30 = -1/u

1/30 = -1/u

u = -30

f= -15

u = -30 = 2f