Ph203 Quiz 14           December 11, 2000

1. Suppose you are sitting at the overlap point between two speakers. Because of destructive interference and the location of the speakers, you hear no sound even though both speakers are emitting identical sound waves. One of the speakers is suddenly shut off. Which of the following describes what you would hear:
   1. There would be no change, you would still hear no sound.
   2. You would hear sound coming from the speaker that was turned off.
   3. You would hear sound coming from the speaker that remained on.
   4. None of the other answers is correct.

   Solution: (c)

2. The tension in a guitar string is doubled. By what factor does the frequency of oscillation of the string change?
   1. It decreases by a factor of 2.
   2. It increases by a factor of 2.
   3. It decreases by a factor of 1.4.
   4. It increases by a factor of 1.4.

   Solution: (d)

3. Diffraction is
   1. the bending of a wave around an obstacle.
   2. the periodic variation in loudness caused by the interference of two sound waves with slightly different frequencies.
   3. what happens when waves that are exactly in phase interfere.
   4. the change in frequency detected by an observer when the source of sound is moving.

   Solution: (a)

4. By blowing across the top of an empty soda bottle, a relatively loud sound can be created because a standing wave develops in the bottle. Why does the pitch of the sound become higher when the bottle is partially filled with water?
   1. The speed of sound in the bottle has increased.
   2. The wavelength of the fundamental tone has decreased.
   3. More overtones are present, hence the overall pitch of the sound is higher.
   4. The speed of sound in water is higher than in air, so the sound wave travels faster in the bottle.

   Solution: (b)

5. A longitudinal standing wave is set up in a tube of air that is open at both ends. If the air in the tube vibrates at the fundamental natural frequency of the tube, what can we say about the pattern of nodes and antinodes in the vibrating air?
   1. There are nodes at each end of the tube.
   2. There are antinodes at each end of the tube and a node at the center.
   3. There is a node at one end and an antinode at the other.
   4. Trick question, air cannot vibrate in a tube that is open at both ends.

   Solution: (b)