An engineer investigates how vibrations from a pump could produce sound inside an air-filled instrument housing.
A vibration source and a vibration detector are used to test two arrangements separately.
Each arrangement is tested in isolation, so the only possible path from the source to the detector is along the rods and across any gap.
The engineer then uses arrangement P. The source produces vibrations of the same amplitude at each tested frequency. The table shows the amplitude of vibration recorded by the detector.
| frequency in Hz\text{Hz}Hz | amplitude of vibration in μm\mu\text{m}μm |
|---|---|
| 200 | 0.30 |
| 400 | 1.20 |
| 800 | 0.75 |
| 1600 | 0.12 |
Explain the difference expected between the detector readings for arrangements P and Q.
The engineer predicts that the amplitude recorded by the detector will decrease whenever the frequency is increased.
Explain whether the results support this prediction.
State which tested frequency should produce the greatest sound intensity inside the instrument housing. Give a reason for your answer.
The source is set to 800 Hz. The vibration at the inner end of the steel rod produces a sound wave in the air inside the housing.
The speed of sound is 5.0 × 103 m/s in steel and 340 m/s in air.
Calculate the decrease in wavelength as the sound passes from the steel into the air.