An object 4 cm in size is placed 20 cm in front of a concave mirror of focal length 10 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image?
A
20 cm from the mirror
B
10 cm from the mirror
C
20/3 cm from the mirror
D
10/3 cm from the mirror
Correct Option:
A
Explanation
The concave mirror has focal length 10 cm, so the object is placed at 20 cm = 2f, the centre of curvature. For a concave mirror, an object at 2f forms a real, inverted image of the same size at 2f. Therefore, the screen should also be placed 20 cm from the mirror.
