(a)[1]
State what is meant by the frequency of an alternating current.
(b)
An alternating current $I$ in a resistor of resistance $680\,\Omega$ changes with time $t$ according to $I = 3.5\sin(40\pi t)$, where $I$ is in A and $t$ is in s.
(b(i))[1]
Show that the period of the alternating current is $50\,\text{ms}$.
(b(ii))[3]
On Fig. 8.1, sketch the variation of $I$ with $t$ between $t = 0$ and $t = 100\,\text{ms}$.
(b(iii))[1]
Determine the root-mean-square (r.m.s.) current in the resistor.
(c)[3]
Use data from (b), including your answer in (b)(iii), to show by calculation that the mean power in the $680\,\Omega$ resistor is half of the peak power.