Page 244 - Basic Electrical Engineering

For the second part of the problem we will use the expression for decaying

current.

i = I e −t/τ
0

We have to calculate t for i to become I /2
0

Therefore,

or,

or,

Therefore t = 0.75 seconds

2.10.3 Transient in R–C Circuit

In Fig. 2.163 is shown a capacitor, C and a resistor, R connected in series

across a dc voltage source, V through a two-way switch S. When the switch S
is connected to position 1, the circuit is switched on. Current i will start
flowing. Let the instantaneous voltage across the capacitor be v , and charge
c
be q. Applying KVL, we can write

V = Ri+ v (i)
c

and

or, q Cv c