Rays from Sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?
(A) 30 cm in front of the mirror
(B) 15 cm in front of the mirror
(C) Between 15 cm and 30 cm in front of the mirror
(D) More than 30 cm in front of the mirror
Answer -
Since rays converge at a point 15 cm from the mirror, then, focal length is 15 cm .
Also, it is concave mirror, focal length will be negative.
Thus,
Focal length = f = -15 cm
Radius of Curvature = C = -30cm
For a Concave mirror
- An object kept at C makes an image of the same size as object
- Thus, the object should be kept at C
So, the correct answer is (a)