480
11 Electrostatics
Fig. 11.16
Fig. 11.17
11.93 Consider a circuit consisting of a resistor R and a capacitor C in series
with a battery of emf ξ and a switch (Fig. 11.17). The capacitor is initially
uncharged and the switch is closed at time t = 0. By considering the potential
drop across each of the components of the circuit, verify that the charge Q
on the capacitor has the form
Q = Cξ
⎛
⎝ 1 − e
−
r
RC
⎞
⎠
(a) What is the current flowing in the circuit?
(b) What is the power supplied by the battery as a function of t?
(c) What is the power dissipated in the resistor as a function of t?
(d) What is the rate at which energy is stored in the capacitor as a function
of t?
[University of Durham 2000]
11.94 For the circuit shown in Fig. 11.18,
(i) What is the initial battery current immediately after switch S is closed?
(ii) What is the battery current a long time after switch S is closed?
(iii) If the switch has been closed for a long time and is then opened, find
the current through the 600 k resistor as a function of time.
Fig. 11.18