Answer: f obs = fv/(v-v s ).
- A f<sub>obs</sub> = f(v-v<sub>s</sub>)/v
- B f<sub>obs</sub> = f(v+v<sub>s</sub>)/v
- C f<sub>obs</sub> = fv/(v-v<sub>s</sub>)
- D f<sub>obs</sub> = fv/(v+v<sub>s</sub>)
Correct answer: C. f<sub>obs</sub> = fv/(v-v<sub>s</sub>)
Explanation: Source moves toward observer: f<sub>obs</sub> = f x v/(v - v<sub>s</sub>). 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.