State, by referring to the power dissipated in a resistor, what the root-mean-square (r.m.s.) value of an alternating voltage means.
State and explain, with reference to the principles of electromagnetic induction, how the increased rotation speed affects the r.m.s. value of the induced e.m.f.
On Fig. 9.1, sketch how the induced e.m.f. $E$ across the coil terminals varies with time $t$ when the rotation speed is increased. Your line should run from time $t = 0$ to time $t = 20\ \text{ms}$. Assume that $E = 0$ at $t = 0$.
A coil rotates freely on frictionless bearings at constant speed in a uniform magnetic field. This rotation produces an induced alternating electromotive force (e.m.f.) across the open terminals of the coil. The induced e.m.f. has an r.m.s. value of $12\,\text{V}$ and a frequency of $50\,\text{Hz}$. The coil’s rotation speed is now doubled.
State and explain what happens to the motion of the coil in (b) when a load resistor is connected across its terminals.