Question

A child travelling in a bus is staring at the wheels of a car. To the child’s amusement the car wheels appear to spin backwards, but the car moves forward. This perception is because of the nature of our human visual sensory system, and is attributed to ..................

• A. aliasing
• B. convolution
• C. filtering
• D. modulation

Hint:

If the sampling rate $f_s<2f$ (signal frequency), perceived frequency folds back as $|f - kf_s|$—the essence of temporal aliasing.

Answer 1

The Correct Option is A

The “wagon-wheel effect” occurs when the temporal sampling (visual frames perceived by the eye/brain, or by a camera) is below twice the wheel’s spoke-passing frequency (violating the Nyquist rate). Under-sampling causes aliasing, which can make the rotation appear slower, stationary, or even reversed.