Question

A light source is attached to a rod fixed in the centre of the ceiling of a square room. It rotates 360° and projects a red beam onto the four walls. Which option correctly shows the beam’s path?

• A. A
• B. B
• C. C
• D. D

Hint:

Always imagine how a rotating point source projects onto flat surfaces. A circle in 3D often appears as sinusoidal or curved traces in 2D projections.

Answer 1

The Correct Option is D

Step 1: Visualize setup.
The light source is at the ceiling center. As it rotates, the beam projects a circular motion around the ceiling edge. When projected onto walls, this circular sweep becomes a curved line.
Step 2: Side view analysis.
From side view, the beam is pivoting from the ceiling midpoint → projects a sinusoidal-like arc along each wall.
Step 3: Compare options.
- (A): Straight wave-like lines, not correct.
- (B): Horizontal line, not correct.
- (C): Flat distribution, not correct.
- (D): Shows curved arcs (parabolic/sinusoidal paths) on each wall, consistent with actual projection.
Step 4: Conclude.
Thus, option (D) is the correct representation. Final Answer: \[ \boxed{\text{D}} \]