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Answers to Quick Quizzes 577 70. A quartz watch contains a crystal oscillator in the form of a block of quartz that vibrates by contracting and expand- Answers to Quick Quizzes 18.1 The shape of the string at t " 0.6 s is shown below. 18.5 (d). Choice (a) is incorrect because the number of nodes is one greater than the number of antinodes. Choice (b) 18.6 For each natural frequency of the glass, the standing wave must “fit” exactly around the rim. In Figure 18.17a we see 1 cm 18.2 (c). The pulses completely cancel each other in terms of displacement of elements of the string from equilibrium, 18.3 (a). The pattern shown at the bottom of Figure 18.9a cor- responds to the extreme position of the string. All ele- 18.4 (d). Near a nodal point, elements on one side of the point are moving upward at this instant and elements on 18.7 (b). With both ends open, the pipe has a fundamental fre- quency given by Equation 18.11: f open " v/2L. With one end closed, the pipe has a fundamental frequency given 18.8 (c). The increase in temperature causes the speed of sound to go up. According to Equation 18.11, this will re- 18.9 (b). Tightening the string has caused the frequencies to be farther apart, based on the increase in the beat frequency. f closed " v 4L " 1 2
v 2L " 1 2
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