Course:PHYS341/Quiz01

Part 1

For questions 1 to 3, fill in the gaps in each paragraph, choosing from the set of words/phrases at the start of each question (each of which may be used more than once) to form the most correct, precise statements.

1 amplitude, medium, frequency, gas, liquid, longitudinal, medium, solid, transverse, wavelength

A pure tone sound wave is a disturbance, generated by something vibrating, propagated through a . The speed of the wave depends entirely on the . The original vibration is preserved throughout the wave, but the will vary if the changes. Our perception of the pitch depends on the of the wave. Our perception of loudness, depends on the and the of the wave.

2 acoustic pressure, acoustic velocity, amplitude, energy, frequency spectrum, integers, pattern, pressure, sound waves, velocity, voltage, wavelength.

The output of a microphone is a that is proportional to . The analog-digital converter in a computer converts this signal into a time-ordered sequence of , which a Fast Fourier Transform (FFT) code converts into another sequence that represents the of the original signal.

3 acoustic displacement, acoustic energy, acoustic pressure, acoustic velocity, amplitude, decreases, even, frequency, half, increases, integer, numbers, odd, radiate, signal, sound waves, spectrum, voltage, wavelength, whole.

An acoustic standing wave exists in a uniform tube, closed rigidly at each end. At each end there must be an node and an antinode. Thus the length of the tube must be an number of wavelengths of the standing wave. If the tube is opened at one end, the fundamental frequency and the open end is an approximate node. The last sentence can only be an approximation, because the open end of the tube can now to the environment.

Part 2

For the following questions, select all statements that are correct. There may be more than one.

1 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

2 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 A taut uniform string, length L, is held rigidly at each end, mounted on a sound board. The string is plucked with a plectrum in the centre of the string. The sound spectrum:

	(a) has two harmonics.
	(b) has one frequency, twice the fundamental frequency.
	(c) has one frequency, half the fundamental frequency.
	(d) has a harmonic spectrum of frequencies 1,3,5,7... times the fundamental frequency
	(e) has a harmonic spectrum of frequencies 2,4,6,8... times the fundamental frequency.

4 Circle all true statements about the concept of acoustic velocity in a wind instrument:

	(a) It is the speed of airflow caused by a player blowing into a wind instrument.
	(b) It is caused by the thermal motion of air molecules which is why wind instruments are out of tune if played cold.
	(c) It is the small collective motion of air molecules at audible frequencies superimposed on motions (a) and (b).
	(d) It has to be zero at the rigid end of a pipe.
	(e) It has to be zero at the open end of a pipe.

5 Circle all true statements concerning the resonant frequencies of a thin bar of wood:

	(a) The thicker the piece (all else being equal), the lower the resonant frequencies.
	(b) The thicker the piece (all else being equal), the higher the resonant frequencies.
	(c) The denser the piece (all else being equal), the lower the resonant frequencies.
	(d) The denser the piece (all else being equal), the higher the resonant frequencies.
	(e) The longer the piece (all else being equal), the lower the resonant frequencies.
	(f) The longer the piece (all else being equal), the higher the resonant frequencies.

Part 3

Point added for a correct answer:
Points for an incorrect answer:
Ignore the questions' coefficients:

1 Sample Question Blue

	The correct answer.
	Distractor.
	Distractor.
	Distractor.

2 Sample Question Green

	The correct answer.
	Distractor.
	Distractor.
	Distractor.