Question

An object is placed at a distance of 10 cm from a concave lens of focal length 20 cm. Find the post
of the image and discuss its nature.
Ans. 6.67 cm on the object side: virtual, erect and smaller than the object

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.