Question

An optical device has been given to a student and he determines its focal length by focusing the image of the sun on a screen placed 24 cm from the device on the same side as the sun. Select the correct statement about the device. (A) Convex mirror of focal length 12 cm
(B) Convex lens of focal length 24 cm
(C) Concave mirror of focal length 24 cm
(D) Convex lens of focal length 12 cm

Answer 1

Answer:

(C) concave mirror of focal length 24 cm

Answer 2

Concave mirror of focal length 24 cm

Explanation:

Given information is that the image of Sun is focused on a screen kept 24 cm away from the mirror/lens.

From the given options, we find that a concave mirror would be the most suitable because the object here, being the sun, is at infinity. And image gets focused at focal point. The concave mirror has the property of forming the image of an object at infinity at the focal point.

Concave mirror is a spherical mirror in which the reflecting surface bulges inwards. A concave mirror is a converging mirror and the incident light rays are reflected inwards towards the focal point. So, these mirrors help focus light.