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Beats/Wave Packets. ConcepTest #33: A note of frequency f 1 is played on a xylophone. A different note f 2 is played on the xylophone at the same time.

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Presentation on theme: "Beats/Wave Packets. ConcepTest #33: A note of frequency f 1 is played on a xylophone. A different note f 2 is played on the xylophone at the same time."— Presentation transcript:

1 Beats/Wave Packets

2 ConcepTest #33: A note of frequency f 1 is played on a xylophone. A different note f 2 is played on the xylophone at the same time. The frequencies of the two notes are close together, but not identical. What will you hear? 1. Nothing. 2.One note, then the other note, in a repeating fashion. 3. Two distinct notes at the same time. 4. A single note that gets louder and softer, repeating. 5. Bach’s Concerto in D minor.

3 ConcepTest #34: Consider a pipe of length L that is open at one end and closed at the other. The pipe can support standing waves of sound. The wavelength of the fundamental (also called the first harmonic or the n = 1 mode) is sketched. What is the wavelength of the next higher harmonic? If this standing wave gives a note of frequency 68 Hz, what is the length of the pipe? The speed of sound in air is 340 m/s. L 1. L /24. 4 L /3 2. 2 L /35. 3 L /2 3. L 6. 2 L

4 ConcepTest #35:

5 Sources of Phase Difference?

6 ConcepTest #36: Two speakers that generate (sound) waves with frequency f = 170 Hz are driven by the same amplifier, so each wave is in phase at the source. The point P is 2 m from one speaker, and 2.75 m from the other speaker. Assume the speed of sound is 340 m/s. a) What is the phase difference between the two waves at the point P?

7 b) Which of the following best represents the phasor diagram for the superposition of the waves at the point P? Two speakers that generate (sound) waves with frequency f = 170 Hz are driven by the same amplifier, so each wave is in phase at the source. The point P is 2 m from one speaker, and 2.75 m from the other speaker. Assume the speed of sound is 340 m/s.

8 c) One of the speakers is disconnected. What happens to the sound at the point P? (Put up one card from each column.) Two speakers that generate (sound) waves with frequency f = 170 Hz are driven by the same amplifier, so each wave is in phase at the source. The point P is 2 m from one speaker, and 2.75 m from the other speaker. Assume the speed of sound is 340 m/s.


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