For a small circuit with open-circuit voltage 14 V and Thevenin resistance 7 Ω, if the load is 14 Ω, what is the voltage across the load?

For a small circuit with open-circuit voltage 14 V and Thevenin resistance 7 Ω, if the load is 14 Ω, what is the voltage across the load?

• A. 9.33 V
• B. 18 V
• C. 4.67 V
• D. 7.0 V

Answer: (A)

In this situation you treat the circuit as a Thevenin source: a 14 V source with a 7 Ω internal resistance in series with the load of 14 Ω. The voltage across the load is found by the voltage divider rule: V_load = V_th × R_load / (R_th + R_load). Compute the total resistance: 7 Ω + 14 Ω = 21 Ω. The current is I = 14 V / 21 Ω = 2/3 A ≈ 0.667 A. The voltage across the load is V_load = I × R_load = 0.667 A × 14 Ω ≈ 9.33 V. Equivalently, V_load = 14 V × 14 Ω / 21 Ω = 9.33 V. So the voltage across the load is about 9.33 V.

In this situation you treat the circuit as a Thevenin source: a 14 V source with a 7 Ω internal resistance in series with the load of 14 Ω. The voltage across the load is found by the voltage divider rule: V_load = V_th × R_load / (R_th + R_load).

Compute the total resistance: 7 Ω + 14 Ω = 21 Ω. The current is I = 14 V / 21 Ω = 2/3 A ≈ 0.667 A. The voltage across the load is V_load = I × R_load = 0.667 A × 14 Ω ≈ 9.33 V. Equivalently, V_load = 14 V × 14 Ω / 21 Ω = 9.33 V.

So the voltage across the load is about 9.33 V.