For the circuit given below, what is the value of Thevenin equivalent resistance (Rth) across the terminals x and y. [Figure description: A left branch with a 1 Ω resistor (current ia flowing down it) at the far left connected via a 1 Ω resistor on the top wire to a middle node. A dependent current source 5ia (arrow pointing up) is connected vertically between the middle node and the bottom wire. From the middle node, a top branch has a 2 Ω resistor in series with a 20 V source going over to terminal x on the right; terminal y is on the bottom wire. Rth is looked into from the x-y terminals.]
- A. +1/2 Ω
- B. -1/2 Ω
- C. 1 Ω
- D. 2 Ω
Answer: B. -1/2 Ω
Explanation: Connecting a test source V across x–y with independent sources killed: ia = V/2 and total current I = ia − 5ia = −4ia = −2V, so Rth = V/I = −1/2 Ω.