A-LevelPhysicsWaves9702/22 · Feb/Mar 2025 · Q55 Marks
A stationary loudspeaker emits sound of constant frequency. A microphone is placed near to the loudspeaker and connected to a cathode-ray oscilloscope (CRO). The trace on the screen of the CRO is shown in [Figure 5.1]. The time-base of the CRO is set to 5.0 × 10⁻⁴ s cm⁻¹.
- (a)The speed of the sound emitted by the loudspeaker is 330ms⁻¹. Determine the wavelength of the sound. wavelength = ................................................................m [3][3]
- (b)The loudspeaker now moves in a straight line while emitting the same sound of constant frequency. The period of the trace on the CRO increases continuously. Describe the motion of the loudspeaker.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2025). The mark or mark type is shown in brackets.
- C1 T = 5.8 × 5.0 × 10-4
- = 2.9 x 10-3
- C1 λ = vT or v = fl and f = 1 / T
- A1 λ = 330 × 2.9 × 10-3 or λ = 330 / 345
- = 0.96 m
- B1 (loudspeaker) moves away (from the microphone)
- B1 at an increasing speed / whilst accelerating
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