Answer: fobs = fv/(v-vs).
- A fobs = f(v-vs)/v
- B fobs = f(v+vs)/v
- C fobs = fv/(v-vs)
- D fobs = fv/(v+vs)
Correct answer: C. fobs = fv/(v-vs)
Explanation: Source moves toward observer: fobs = f x v/(v - vs). Denominator decreases, so observed frequency increases.
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.