Question

A flat mirror M is arranged parallel to a wall W at a distance 1m from it. The light produced by a point source S kept on the wall is reflected by the mirror and produces a light spot on the wall. The mirror moves with velocity v towards the wall.

• A. The spot of light will move with the speed v on the wall.
• B. The spot of light will not move on the wall.
• C. As the mirror comes closer the spot of light will become larger and shift away from the wall with speed larger then v.
• D. The size of the light spot on the wall remains the same.

Answer 1

Answer: (B), (D)

The correct options are
B The spot of light will not move on the wall.
D The size of the light spot on the wall remains the same.

Since the mirror M is perfectly parallel to the wall W, its distance from the wall does not matter for the light spot. So the spot light will remain stationary. Also the source being point source, the image size will also remain a point.

Hence correct Answer are option B, D