Question

A student determines the focal length of a device X by focusing the image of a distant object on the screen placed on the same side of the object.The device X is:-

a)Cocave lens

b)Convex lens

c)Concave mirror

d)Convex mirror

Answer 1

Concave mirror because same of the object and also a screen is required

Answer 2

Answer: The device X is the (c). concave mirror.

Explanation:

The concave mirror is placed at the focal length of 20 centimeter. The concave mirror give the formation of the image on the same side on the same screen where its focus point lies when the object is kept at distance.

So this is why the concave mirror must be kept at 20 centimeter to give the image mentioned in the question.