Question

A bar of length 10 cm is placed horizontally before a concave mirror having radius of curvature 20 cm. Total length of the image will be

Answer 1

The object lies horizontally on the principal axis. So let the object be AB. B lies 20 cm away from the pole and A lies 10+20 = 30 cm away from the pole.

C = 2f = 2(10). Center of Curvature is 20 cm. So point B is at center of curvature and so the image formed will be 20 cm away from the mirror(in the left side). OR you can also verify this with mirror formula.

Image of Point A will be formed at = 1/v + 1/u = 1/f

1/v = 1/f - 1/u

1/v = 1/-10 -1/-30 = -2/20

v = -30/2 = -15.

So image of point A will be at 15 cm in left side of mirror. Now callculate the length of the image. It is equal to 20 - 15 = 5. Image distance of B - Image distance of A