State two differences between the e.m.f. of a battery and that of an alternating current (a.c.) power supply.
The circuit has three resistors and two open switches, $S_1$ and $S_2$. Figure 9.1 shows the arrangement. $YZ$ is a straight horizontal wire segment positioned between two magnets. $S_1$ is closed now. Calculate the current in $YZ$.
Explain why a force acts on $YZ$.
Tick the box that shows the direction of the force on $YZ$.
Explain how the direction of the force on $YZ$ is found.
With switch $S_2$ also closed in Fig. 9.1, Calculate the total resistance of the circuit.
Explain what happens to the force acting on $YZ$ when switch $S_2$ is closed.
The current through the $20\,\Omega$ resistor is $I_{20}$. The current through the $30\,\Omega$ resistor is $I_{30}$. State a value for the ratio $I_{20} / I_{30}$.