exam2soln - 1 Physics 198 EXAM 2 Oct. 29, 2009 The exam is...

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1 1 Physics 198 EXAM 2 Oct. 29, 2009 The exam is closed book, although you may use a single sheet of paper to aid memory. (You may use the sheet from the first exam as well.) For multiple choice questions, mark the answer you believe is MOST CORRECT on the exam. Please turn in only the exam sheets, not your formula sheets. There are 24 problems, each worth 2 points. Note that the numbers labeling the octave change on C, e.g., A 3 , A # 3 , B 3 , C 4 , C # 4 , etc., with C 4 being middle C. An artist has constructed a sculpture out of steel. It is suspended by a thread, and it rings when struck gently with a metal bar. A Physics 198 student carrying a microphone attached to a computer using SpectraPlus, records the following sound spectrum just after the sculpture is struck. The first two questions refer to this figure.
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2 2 1) Which of the five peaks in the spectrum corresponds to the normal mode with the highest Q? => Peak c. A higher Q implies a narrower peak in the spectrum. Peak c will also ring longer than the other modes of the sculpture because of its high Q. 2) The frequencies of peaks in the spectrum are approximately: 0.5 kHz, 1.3 Hz, 1.7 kHz, 2.7 kHz and 3.6 kHz. Mark the following statements as true or false. a. The peaks at b, c, d and e are correctly described as the second, third, fourth and fifth harmonics of the peak at a. (True or False ) Not integer multiples. b. The peaks at b, c, d and e are correctly described as the first, second, third and fourth overtones of the peak at a. ( True or False) ________________________________________________________________________________________ 3) Give an example of the phenomenon of resonance as used in this course. (You could, for example, describe of the examples from lecture or from lab.) i) Transfer of energy from two identical tuning bars widely separated in the lecture. ii) Excitation of resonances in an open/open (or open/closed) tube in Lab with speaker at right frequency. iii) Excitation of resonances on a string by a vibrator when string tension was just right. iv) Blocks of the same mass supported by differing length wires on a piece of wood as used in lecture. Blocks supported by wires of same length transferred energy efficiently, etc. 4) In Lab 6 you studied the normal modes of a tuning fork by viewing its spectrum. For a 440 Hz tuning fork the fundamental frequency peak will, of course, be at 440 Hz and you might also see a weaker peak at about 880 Hz. In addition you will sometimes see a peak from the “clang” mode, particularly if you strike the fork with something hard. From your experience in the lab, at what frequency would you
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exam2soln - 1 Physics 198 EXAM 2 Oct. 29, 2009 The exam is...

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