Physics 3200: Heat, Light and Sound

Homework Assignment 8: Turn in the questions below on Monday, May 12.

Unless told otherwise, assume the speed of sound in air is 340m/s.

1. What are a compression and a rarefaction? How do they relate to sound waves?

2. What is an echo?

3. What factors determine the natural frequency of an object? (If you increase each of them, how will the natural frequency change, i.e. will the natural frequency increase or decrease?)

4. Can two waves cancel each other? If so, give an example.

5. You see a flash of lightening and hear the thunder from in 8s later. If the lightening was 2.5km away, what is the speed of sound? (Don’t assume it is 340m/s in this case.)

6. Explain how a loudspeaker produces sound waves.

7. What is resonance? Give an example of resonance.

8. If a bat emits an ultrasonic pulse (a high frequency sound wave) and hears the echo from a cliff 0.06s later, how far away is the cliff?

9. The speed of a wave on a string is 40m/s and the frequency of a wave is 80Hz. What is the wavelength?

10. The picture below shows the vibration of a string of length 1.2m. Points on the string vibrate between the solid and dashed lines.

a) What is the wavelength of this wave?

b) If the frequency is 120Hz, what is the wave speed?

c) Which harmonic or mode of vibration is this, the 1^st, 2^nd, 3^rd, 4^th, etc.?

11. The picture at the right shows a wave traveling down a string. If the wave speed is 40m/s, what is the frequency of this wave?