Course:PHYS341/Archive/2016wTerm2/Assignments/A4

Practice Questions for Quiz 4, Friday Feb 10

Textbook sections covered: 8.1-8.2, 8.8; 9.2-9.4; 10.1-10.3; 11.1-11.3

1. Circle statements that are correct:

(a) A pure sine wave has a simple spectrum with just one frequency. ✓
(b) Any repeated waveform has a spectrum consisting of partials whose frequencies are integer multiples of a fundamental frequency. ✓
(c) The less a repeated waveform looks like a simple sine wave, the richer the spectrum (i.e. many strong partials). ✓
(d) A repeated waveform that does not look like a sine wave has partials that are not integer multiples of a fundamental frequency.
(e) A waveform of random but endlessly repeated shape has a random spectrum.
(f) A waveform of random but endlessly repeated shape has a spectrum consisting of partials whose frequencies are integer multiples of a fundamental frequency. ✓

2. A siren in the middle of an open field produces a pure tone at 3 kHz. You listen at the edge of the field. Now the tone changes frequency to 10 kHz with no change in acoustic power. What you hear is:

(a) Quieter ✓
(b) Louder
(c) Neither quieter nor louder

The tone changes back to the original 3 kHz, and then moves to 100 Hz, again with no change in acoustic power. What you hear is:

(d) Quieter ✓
(e) Louder
(f) Neither quieter nor louder

3. Two pure tones in the middle of piano range, a semitone apart (say concert A and A♯ i.e. 440 and 466 Hz) sound rough together because:

(a) semitones sound bad together
(b) the tones are beating together and so the excited area of the basilar membrane never settles down.
(c) the waveform is no longer repetitive and so the excited area of the basilar membrane never settles down.
(d) the tones excite areas of the basilar membrane that are too close together for the brain to figure out the central frequency. ✓

4. A taut uniform string, length L, is held rigidly at each end, mounted on a sound board. The string is plucked with a plectrum at a distance L/3 from one end. The sound spectrum:

(a) has three harmonics.
(b) has one frequency, three times the fundamental frequency.
(c) has one frequency, one third of the fundamental frequency.
(d) has a harmonic spectrum of frequencies 1,2,4,5,7,8,10,11... times the fundamental frequency. ✓
(e) has a harmonic spectrum of frequencies 3,6,9,12... times the fundamental frequency.