At What Distance From Concave Mirror Of Focal Length 10 Cm Should Object Be Placed So That

At what distance from a concave mirror of focal length 10 cm should an object be placed so that: … virtual image is formed 20 cm…

Answers:

(a) f = -10 cm

v = – 20 cm (real image)

1/v + 1/u = 1/f

1/-20 + 1/u = 1/-10

1/u = -1/10 + 1/20 = -1/20

u = -20 cm

(b) f = -10 cm

V = 20 cm (virtual image)

1/v + 1/u = 1/f

1/20 + 1/u = 1/-10

1/u = -1/10 + -1/20 = -3/20

u = -(20/3) cm