Am. (a) Probably at first the sound of the fork would not be much altered, but as the water is gradually poured in, the sound will gradually increase in intensity up to a maximum and then fall off again. If the cylinder is long enough and the water is still gradually poured in, this effect may be repeated. For explanation, see pp. 61 and 62. For explanation of repetition, it will be seen from pp. 61 and 62 that resonance takes place when length of vibrating column is i» t> or i» &c-> tQe length of sound-wave, but the maximum intensity is obtained in first case.
(b) First ascertain by repeated trials, the length of air column that gives maximum resonance ; measure this length ; add to it £ radius of cylinder; multiply four times this result by the vibration number of the fork.
8. (a) Discuss the relative consonance of an octave, a fourth, and a minor third.
(b) Why is it that in any system of temperament, the octaves must be true, whilst the minor thirds may be considerably different from true minor thirds ?
Am. (a) See pp. 187, 188, 189, 191.
(b) This follows from the perfect definition of the octave and the vague definition of the minor third. See pp. 177 and 181.
9. Two tuning-forks very nearly an octave apart and free from overtones give beats when sounded together. What is the cause of the beats ?
Am.—Say vibration numbers of forks are 202 and 400. These generate a third tone the vibration number of which = 198 ; and this with the lower fork produces 202—198 = four beats per sec.
May 26, 1896. 9 till 12.
1. (a) Explain the meaning of the terms—simple harmonic vibration, wave front, difference of phase, wave length.
(J) Give a diagram illustrating the motion of a series of particles as a transverse wave passes over them.
(<?) Show that the wave length is equal to the velocity of the wave multiplied by the time of vibration of one of the particles.