Since the resistors are connected in series, we know that
the same amount
of current goes through each one. Furthermore, we know that the total
resistance
is just the sum of the resistances. Therefore, RTotal
= 4 W + 8 W + 12 W
= 24 W. The current
through the circuit is given by I = V/RTotal =
24 V/24 W = 1 amp.
2
(a) The time constant for an RC circuit is given by t = RC. For this problem, we get t = (2.0 x 106
V)(6.0 x 10-6 F)
= 12 s.
(b) The maximum charge on the capacitor is determined
only by the size of the capacitor, i.e. Q = CV. For the values given,
this means that Qmax = (6.0 x 10-6
F)(20 V) = 1.2 x 10-4 C.