What is the time constant of the circuit shown below, when t = 0 the Switch S is closed? [Figure description: A 10 V battery on the left. Top wire: a 2 Ω resistor in series with switch S (closes at t = 0) leading to the right side. Middle wire: from the battery's positive rail, a 2 Ω resistor then a node with a 20 µF capacitor going down to the bottom rail, then another 2 Ω resistor continuing to the right-hand node. Right vertical branch: a 2 Ω resistor from the top-right corner down to the bottom rail. The top wire (through the switch) joins the right-hand node above the 2 Ω vertical resistor.]
- A. 26.67 µSec
- B. 80 µSec
- C. 16 µSec
- D. 24 µSec
Answer: D. 24 µSec
Explanation: With switch S closed at t = 0, Thevenin resistance seen across the capacitor is Rth = 1.2 Ω, giving time constant τ = Rth·C = 1.2 × 20 µF = 24 µs.