Question

The focal length of a camera is 20 cm . Find how far away from the film must the lens be set in order to photograph an object located at a distance of 100 cm from the lens.​

Answer 1

f = 20 cm

u = 100 cm

v = ???

By formula ,

1/f = 1/v + 1/u

1/20 = 1/v + 1/100

1/20 - 1/100 = 1/v

100 - 20 / 2000 = 1/v

80 / 2000 = 1/v

4/100 = 1/v

v = 100/4

v = 25 cm Ans...