Define open-circuit voltage and explain its significance in Thevenin equivalents.

Define open-circuit voltage and explain its significance in Thevenin equivalents.

• A. V_OC is the voltage when the load is shorted; it equals I_sc times R_th.
• B. V_OC is the voltage across the output terminals with no load; it equals V_th in Thevenin equivalents.
• C. V_OC is always zero.
• D. V_OC is the maximum load voltage delivered.

Answer: (B)

Open-circuit voltage is the potential difference across the output terminals when nothing is connected to the output (no load current flows). It tells you the voltage the network would deliver to a load if you could remove any loading effects. In a Thevenin equivalent, this open-circuit voltage becomes the Thevenin voltage, V_th. The network is then modeled as a voltage source of V_th in series with an internal resistance, R_th. That’s why V_th equals the open-circuit voltage. This sets the baseline for how the load voltage behaves: with a load RL, the voltage across the load is V_L = V_th · (R_L / (R_th + R_L)), and in the limit of no load (R_L → ∞) you recover V_L → V_th. Additionally, the short-circuit current satisfies V_th = I_sc · R_th, linking V_oc, I_sc, and R_th in the Thevenin model.

Open-circuit voltage is the potential difference across the output terminals when nothing is connected to the output (no load current flows). It tells you the voltage the network would deliver to a load if you could remove any loading effects. In a Thevenin equivalent, this open-circuit voltage becomes the Thevenin voltage, V_th. The network is then modeled as a voltage source of V_th in series with an internal resistance, R_th. That’s why V_th equals the open-circuit voltage. This sets the baseline for how the load voltage behaves: with a load RL, the voltage across the load is V_L = V_th · (R_L / (R_th + R_L)), and in the limit of no load (R_L → ∞) you recover V_L → V_th. Additionally, the short-circuit current satisfies V_th = I_sc · R_th, linking V_oc, I_sc, and R_th in the Thevenin model.