Question

an object is placed 20 cm infront of a concave mirror of focal length 15 cm .object is 3 cm high calculate the position and size of image

Answer 1

Given ::- object dist. (u) = 20cm

Focal length (f) = 15cm

Ht. of object = 3cm

To find ::- position and size of the image

Solution ::-

Mirror formula --

1/v + 1/u = 1/f

1/v + 1/(-20) = 1/(-15)

1/v - 1/20 = -1/15

1/v = -1/15 + 1/20

1/v = 1/20 - 1/15

1/v = 3 - 4/60

1/v = - 1/60

v = -60 cm

Therefore , the image distance is -60cm

But the 2f = -30cm

That is the image formed beyond center of curvature.

h' /h = -v/u

h' / (3) = - (-60)/20

h' /3 = 60/20

h' /3 = 3

h' = 3 x 3

h' = 9cm

Therefore the ht. of image is 9cm, which is larger than the object ht.

HOPE IT HELPS YOU!!