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Capacitors - Technical MCQs

Q1:

If a capacitor is placed across a 20 V source, what will be the amount of charge after 5 tc?

A 5.0 V

B 12.8 V

C 13.5 V

D 20 V

ANS:D - 20 V

Given: Time constant (T / Æ®) = (T / RC) = 5 TC. (Æ®) = RC. VC = [VIN (1- e^-(T/(R*C))]. VC = [20 * (1- e^-(T/ Æ®)]. VC = [20 * (1- e^-(5))]. VC = [20 * (1- e^-(5))]. [Where: e^1 = 2.7182; e^-5 = (1/e5) = [1 / (2.7182)^5] = [1 / 148.41]= 0.0067]. VC = [20 * (1- 0.0067)]. VC = [20 * (0.9933)] = 19.866 V. VC = 19.866 V => 20 V.