Question: What is the voltage across a capacitor after 3 time constants in an RC circuit with a supply voltage of 12 V?

Options:

1. 12 V
2. 8 V
3. 4 V
4. 0 V

Correct Answer: 8 V

Solution:

Voltage across capacitor V(t) = V0 * (1 - e^(-t/τ)). After 3τ, V(3τ) = 12 V * (1 - e^(-3)) ≈ 12 V * (1 - 0.05) ≈ 11.4 V.