Question

A resistor R and 2 μF capacitor in series is connected through a switch to 200 V direct supply.

Answer 1

v = 200(1 - e-t/τ)

120 = 200(1 - e-t/τ)

e-t/τ = (200 - 120)/200 = 80/200

-t/τ = log(2.5) = 0.4

5 = 0.4 x R x 2 x 10-6

R = 5/(0.6 x 2 x 10-6)

R = 2.7 x 106