Question Answers

Pipes and Strings

1. A tuning fork produces a feeble sound. But when it is pressed against a table, a loud sound is heard. Why?

The loudness of sound depends on the surface area of the region available for vibration. When the tuning fork is struck against a rubber pad, the vibration of prongs causes vibration of air of a small area, which makes it appear feeble. But when it stem is pressed against a tabletop, the whole of the top vibrates and causes the vibration of large area of air. This makes it appear loud.

2. Why are all string instruments provided with hollow boxes

The loudness of sound depends on the surface area of the region available for vibration. The string vibrating between two fixed ends causes vibration of air of a small area, which makes it feeble. If the sounding board (hollow box) is provided then the strings as well as the air inside the board is set into vibrations. As the board is of large surface, it transmits more energy into the air and loud sound is heard.

3. A loud sound is heard at resonance. Why?

At resonance, the frequencies of the applied oscillating force and the vibrating body are same and the amplitude of the resultant vibrations will be highest at such condition. Thus the intensity of sound produced that depends on the amplitude of vibration will be greatest and hence, the sound is heard loud.

4. Is it possible to have a longitudinal wave on a stretched string? Why or why not?

Yes, it is possible to have a longitudinal wave on a stretched string. When the stretched string is stroked along its length, a longitudinal wave is produced. The compression and rarefaction travels along the length and reflected back from the end giving rise to stationary waves.

5. Is the wave speed the same as the speed of any part of the string for transverse waves? Explain the difference between these two speeds.

The wave speed is different from the velocity of the particle oscillating in the string. These oscillating particles give rise to the formation of wave. The particle velocity varies with the position of the particle in the space but wave velocity propagates with a constant speed. Hence, the wave speed is not the same as the speed of any part of the string for transverse waves.