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Waves and sound
5 NET Physics questions with answers and explanations.
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A string has a tension of 100 N and a mass per unit length of 0.01 kg/m. What is the speed of a wave on it?
- 1 10 m/s
- 2 100 m/s
- 3 1000 m/s
- 4 50 m/s
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Correct answer: 100 m/s
v = sqrt(T / mu) = sqrt(100 / 0.01) = sqrt(10000) = 100 m/s.
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What is the fundamental frequency of an open pipe 1 m long? (Speed of sound 340 m/s)
- 1 85 Hz
- 2 170 Hz
- 3 340 Hz
- 4 680 Hz
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When the intensity of a sound is doubled, the sound level rises by about:
- 1 1 dB
- 2 3 dB
- 3 6 dB
- 4 10 dB
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Correct answer: 3 dB
The level is 10 log(I2 / I1) = 10 log 2, which is about 3 dB.
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An observer moves towards a stationary source of sound. The frequency heard is:
- 1 Lower than the source frequency
- 2 Higher than the source frequency
- 3 The same as the source frequency
- 4 Zero
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Correct answer: Higher than the source frequency
The observer meets the wave fronts more often, so the apparent frequency is higher.
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In a standing wave, the distance between two adjacent nodes is:
- 1 One wavelength
- 2 Half a wavelength
- 3 A quarter of a wavelength
- 4 Two wavelengths
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Correct answer: Half a wavelength
Nodes are separated by half a wavelength, and antinodes lie midway between them.