Question

An object of height 10 cm is placed at a distance of 20 cm from a concave lens of focal length 25 cm.
(a) Calculate the distance of image formed from the lens.
(b) Calculate the height of image.
© Is the image real or virtual? Justify your answer.

Answer 1

Explanation:

Given:

Focal length of concave mirror, f = -20 cm

Distance of object from the mirror, u = -10 cm

use formula, 1/v + 1/u = 1/f

or, 1/v = 1/f - 1/u

or, 1/v = 1/-20 - 1/-10

or, 1/v = -1/20 + 1/10 = 1/20

or, v = +20cm

hence, image position is the 20cm right side from the pole of the concave mirror as shown in the diagram. The image is straight and bigger than the object.