If the load resistance in a Thevenin circuit with V_th = 9 V and R_th = 3 Ω is increased, what happens to the load current?

• A. Increases
• B. Remains the same
• C. Becomes negative
• D. Decreases

Answer: (D)

In a Thevenin circuit, the load current is determined by the total resistance the source sees, which is the sum of the Thevenin resistance and the load resistance. With Vth = 9 V and Rth = 3 Ω, the load current is I = Vth / (Rth + R_L) = 9 / (3 + R_L) amperes. As the load resistance increases, the denominator grows, so the current decreases. For example, increasing R_L from 3 Ω to 6 Ω changes the current from 1.5 A to 1 A. The current wouldn’t stay the same or become negative under these positive, passive conditions. So the load current decreases when the load resistance increases.