1© Manhattan Press (H.K.) Ltd Stationary waves in air

2 © Manhattan Press (H.K.) Ltd Stationary waves in air (SB p. 141) Stationary waves in air Stationary waves in air obtained by: sound wave from loudspeaker is reflected superposition of waves v = 2fd Go to Example 6 Example 6

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4 © Manhattan Press (H.K.) Ltd. Q: Q:S 1 and S 2 are two loudspeakers which emit sound waves of frequency Hz continuously. M is a small microphone which is moved along the line joining S 1 and S 2 with a speed of 30 m s –1. (a) The sound received by M rises and falls periodically. Explain why. (b) If the speed of sound is 330 m s –1, calculate the frequency of the rise and fall in the sound received by M. Solution 10.3 Stationary waves in air (SB p. 142)

5 © Manhattan Press (H.K.) Ltd. Solution: 10.3 Stationary waves in air (SB p. 142) (a) Sound waves from S 1 and S 2 are of the same frequency and amplitude but travelling in opposite directions. The superposition of the waves produces a stationary wave between S 1 and S 2. At the antinodes of the stationary wave, the vibration is of large amplitude and a loud sound is detected by the microphone. At the nodes, the amplitude is zero and no sound is detected. (b) Frequency, f = Hz, speed of sound v = 330 m s –1 Return to Text