Question

A concave lens has a focal length of 20cm. At what distance from the lens a 5cm tall object be placed so that it form an image at 15cm from the lens? Also, calculate the size of the image formed

Answer 1

Answer:

focal length (f) = -20cm

object distance (u) = ?

image distance (v) = 15cm

1/f =1/v - 1/u

1/-20 = 1/15 - 1/u

1/u = 1/-20 - 1/15

1/u = 15+20/-20×15

1/u = 35/-300

u = -0.1166