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Sound: speed, pitch and loudness
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Sound is a longitudinal wave. An oscilloscope shows sound waves so you can measure their frequency.
Sound waves
Sound waves are longitudinal. Like all waves, they can be reflected (echoes) and refracted.
The human hearing range is about 20 Hz to 20 000 Hz.
Measuring the speed of sound: stand a measured distance (such as 100 m) from a friend who bangs two blocks together. Start a timer when you see the bang and stop it when you hear it. speed = distance ÷ time. Repeat and average. The speed of sound in air is about 330 to 340 m/s.
The human hearing range is about 20 Hz to 20 000 Hz.
Measuring the speed of sound: stand a measured distance (such as 100 m) from a friend who bangs two blocks together. Start a timer when you see the bang and stop it when you hear it. speed = distance ÷ time. Repeat and average. The speed of sound in air is about 330 to 340 m/s.
Using an oscilloscope
A microphone turns sound into an electrical signal, which an oscilloscope shows as a wave.
The horizontal axis is time. Find the time for one complete wave (the period, T) from the number of squares × the timebase setting.
f = 1 ÷ T
Example: one wave covers 4 squares at 0.5 ms per square. T = 2 ms = 0.002 s, so f = 1 ÷ 0.002 = 500 Hz.
The horizontal axis is time. Find the time for one complete wave (the period, T) from the number of squares × the timebase setting.
f = 1 ÷ T
Example: one wave covers 4 squares at 0.5 ms per square. T = 2 ms = 0.002 s, so f = 1 ÷ 0.002 = 500 Hz.
Pitch and loudness
Pitch depends on frequency: a higher frequency vibration gives a higher pitch. On screen, waves are closer together.
Loudness depends on amplitude: a bigger amplitude vibration gives a louder sound. On screen, waves are taller.
Loudness depends on amplitude: a bigger amplitude vibration gives a louder sound. On screen, waves are taller.
A student stands 165 m from a starting pistol. She hears the bang 0.50 s after she sees the flash. What is the speed of sound?
- speed = distance ÷ time
- 165 ÷ 0.50
Answer: 330 m/s
Sound is longitudinal. Humans hear 20 Hz to 20 000 Hz. Measure the speed of sound with distance ÷ time. An oscilloscope shows the wave: period from squares × timebase, f = 1 ÷ T. Higher frequency means higher pitch; bigger amplitude means louder.
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