Question

A 8 microF capacitor is connected in series with a 0.5 megaohm resistor. The DC voltage supply is 200V. Calculate the time taken for the potential difference across the capacitor to grow to 160V.

(a) 6.93s

(b) 7.77s

(c) 2.33s

(d) 3.22s

This question was addressed to me in unit test.

I want to ask this question from Discharge of a Capacitor Through a Resistor in portion Capacitance and Capacitors of Basic Electrical Engineering

Answer 1

The correct answer is (a) 6.93s

Easy explanation: From the previous explanations, we know that the initial current is 400mA and the time constant is 4s. Substituting the values of capacitor voltage, initial voltage, initial current and time constant in the equation: V=V0(1-e^-t/RC)

Substituting V=160V, V0=200V, RC=4s we get,

t=6.93s.