The circuit shown in Figure 20.67 is composed of two batteries, two identical thin-filament bulbs, and an initially uncharged
capacitor. Three compasses are placed on the desktop underneath the wires, all pointing north before the circuit is closed.
Then the gap in the wire is closed, and the compass on the left immediately shows about a 20° deflection.
(a) On a diagram, draw the new needle positions on all three compasses at this time, and write the approximate angle of
deflection beside the compasses labeled A and B. Explain carefully.
(b) When this circuit was connected with one of the bulbs removed from its socket, the single bulb glowed for T
seconds. In the two-bulb circuit shown in Figure 20.67, predict how long the two bulbs would glow (in terms of T).
Explain carefully.
(c) If possible, carry out the experiment, observing initial compass deflections and length of time of glow with one or
two thin-filament bulbs. State your numerical results. Do your observations agree with your predictions?