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A Levels Physics (9702)•9702/11/M/J/19
Question 27 from 9702/11/M/J/19

Explanation

Stationary Wave Node Separation

Steps:

  • In a stationary wave, distance between adjacent nodes is λ/2, where λ is the wavelength of the progressive waves.
  • Given node separation of 1.5 m, λ/2 = 1.5 m, so λ = 3 m.
  • Frequency f = 300 Hz.
  • Wave speed v = f λ = 300 × 3 = 900 m/s.

Why D is correct:

  • Speed v = f λ follows the wave equation, with λ = 2 × node separation = 3 m, yielding 900 m/s.

Why the others are wrong:

  • A: 100 m/s gives λ = 100/300 ≈ 0.33 m, node separation ≈ 0.17 m (too small).
  • B: 200 m/s gives λ ≈ 0.67 m, node separation ≈ 0.33 m (too small).
  • C: 450 m/s gives λ = 1.5 m, node separation = 0.75 m (half of 1.5 m).

Final answer: D

Topic: Stationary waves

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