CET DC Circuit Analysis & Theory 5

Question 1

A 100 μF capacitor is connected in series with a 10 kΩ resistor and a 50 V DC source. What is the time constant (τ) of the circuit?

Accepted Answer

1 s

Answer

τ = RC = 10,000 × 100×10⁻⁶ = 1 s.

Question 2

After one time constant (τ), a charging capacitor reaches approximately what percentage of the supply voltage?

Accepted Answer

63%

Answer

V(τ) = V_s(1 − e⁻¹) ≈ 0.632 × V_s, so approximately 63%.

Question 3

In a fully charged capacitor in a DC steady-state circuit, what current flows through it?

Accepted Answer

Zero

Answer

At steady state, the capacitor voltage equals the source voltage and no current flows (capacitor acts as an open circuit).

Question 4

Which of the following correctly describes the energy stored in a capacitor?

Accepted Answer

E = ½CV²

Answer

The energy stored in a capacitor is E = ½CV², where C is capacitance and V is voltage across it.

Question 5

Two capacitors of 4 μF and 6 μF are connected in series. What is the equivalent capacitance?

Accepted Answer

2.4 μF

Answer

1/C = 1/4 + 1/6 = 5/12; C = 12/5 = 2.4 μF.

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