Answer: Source or observer is moving.
- A Amplitude changes
- B Wavelength changes in medium
- C Source or observer is moving
- D Wave enters a new medium
Correct answer: C. Source or observer is moving
Explanation: Doppler effect: when source or observer moves, the observed frequency differs from emitted frequency.
A standing wave forms from two identical waves travelling in opposite directions and interfering; nodes (always zero displacement) and antinodes (maximum displacement) stay fixed in place, unlike a travelling wave where the whole pattern moves.
Concept context
Wave types, superposition, standing waves, Doppler effect, and sound intensity.