270 RAND-BOOK OF ACOUSTICS,
ROYAL. UNIVERSITY OF IRELAND. MUS. Bac. First Examination, 1895.
1. Male and female voices differ in pitch and quality. Acount for these differences.
Am.—The larynges of women are smaller than those of men, the vocal cords are smaller and vibrate more quickly, hence the difference in pitch. When a man and a woman are singing a tone of same pitch and with about the same intensity there is no specific difference of quality. A man's low tones are richer in partials than a woman's high tones, hence the corresponding difference in quality.
2. (a) What is meant by the wave-length of a note ?
(J) When sound passes from one medium to another (as from one gas to another of different density), what change, if any, takes place in the wave-length ?
Am. (a) See p. 22.
(b) The velocities of sound in different gases vary inversely as the square roots of their densities. (See p. 20.) Therefore when a sound passes from one gas into another of greater density its velocity is diminished. Now the wave length equals the velocity divided by the vibration number (see p. 39); therefore, in this case, the wave-length is diminished. Similarly, if a sound passes into a gas of less density its wave-length is increased.
3. Describe a method of accurately determining the velocity of sound through air.
Am.—See p. 268.
The result will be the more accurate, the farther the experimenters are apart. It will also be more exact, if each observer make a signal, say fires a cannon and both note the time between the flash and the report, the mean of the two observations being taken.
4. (a) The temperature of air through which sound-waves are propagated is supposed to be subject to changes of an alternating character.
Describe the nature of these changes, and give an explanation of them.
(b) Is there any change of temperature of a continuous character, and if eo, to what would you attribute it P
Am. (a) When a gas is compressed, its temperature rises, heat being evolved ; when a gas expands freely, its temperature falls. Hence the temperature of the air through which a sound-wave passes rises very slightly at a point through which a condensation is passing, and falls very slightly when the rarefaction follows.