Page 250 - Basic Electrical Engineering

Thus, for a time equal to time constant τ, both capacitor voltage v and the
c
circuit current i are reduced to 36.8 per cent of their initial values with initial

rate of decay remaining unchanged.

Figure 2.165 Transients in RC circuit, decay of voltage across the charged capacitor and the circuit
current

Example 2.53 A capacitor of value 1 μF and a resistor of 5.45 MΩ are
connected in series across a 220 V dc supply through a switch. Calculate the

time by which the capacitor will be charged to 60 per cent of the supply
voltage.

Solution:

−6
6
R = 5.45 × 10 Ω, C = 1 × 10 F
−6
Time constant, τ = RC = 5.45 × 106 × 1 × 10 sec
= 5.45seconds