Alternating Quantities 207 Worked Example 6.6 Q A non-sinusoidal waveform has a peak factor of 2.5, and an r.m.s. value of 240 V. It is proposed to use a capacitor in a circuit connected to this supply. Determine the minimum safe working voltage rating required for the capacitor. A peak factor ; V voltso, V2 52402525240600...VVVVmm Thus the absolute minimum working voltage must be 600 V Ans In practice, a capacitor having a higher working voltage would be selected. This would then allow a factor of safety. 6.7 Form Factor As the name implies, this factor gives an indication of the form or shape of the waveform. It is deﬁ ned as the ratio of the r.m.s. value to the average value. Thus, for a sinewave ,form factorr.m.s. valueaverage valueso, form f0 7070 637..aactor111. For a rectangular waveform (a squarewave), form factor 1, since the r.m.s. value, the peak value, and the average value are all the same. Worked Example 6.7 Q A rectangular coil, measuring 25 cm by 20 cm, has 80 turns. The coil is rotated, about an axis parallel with its longer sides, in a magnetic fi eld of density 75 mT. If the speed of rotation is 3000 rev/min, calculate, from fi rst principles, (a) the amplitude, r.m.s. and average values of the emf, (b) the frequency and period of the generated waveform, (c) the instantaneous value, 2 ms after it is zero. A 0 250 2800 07530006020 3...m; m; ; T rev/s; sdNBnt1 (a) e 2 NBℓv sin (2 ft ) volt Now, we know the rotational speed n , but the above equation requires the tangential velocity, v , in metre per second. This may be found as follows.