To determine V_th in Thevenin analysis, what is the first step?

To determine V_th in Thevenin analysis, what is the first step?

• A. Remove the load and measure the open-circuit voltage to find V_th.
• B. Short the load and measure the voltage.
• C. Short the load and measure the current.
• D. Replace the load with a known resistor.

Answer: (A)

V_th is the voltage across the output terminals when nothing is connected to the load. To determine it, remove the load and measure the voltage with the circuit open. With no current flowing, there’s no drop across the internal resistances, so the terminal voltage equals the source voltage. That open-circuit measurement directly gives V_th. Shorting the load would force current and collapse the terminal voltage toward zero in many cases, so it does not yield V_th. Measuring the current under a short gives the short-circuit current, which relates to the Thevenin resistance, not the open-circuit voltage. Replacing the load with a known resistor isn’t the method for finding V_th; it’s a different step that could be used later to characterize the circuit’s behavior, but the standard first step to find V_th is open-circuit measurement.

V_th is the voltage across the output terminals when nothing is connected to the load. To determine it, remove the load and measure the voltage with the circuit open. With no current flowing, there’s no drop across the internal resistances, so the terminal voltage equals the source voltage. That open-circuit measurement directly gives V_th.

Shorting the load would force current and collapse the terminal voltage toward zero in many cases, so it does not yield V_th. Measuring the current under a short gives the short-circuit current, which relates to the Thevenin resistance, not the open-circuit voltage. Replacing the load with a known resistor isn’t the method for finding V_th; it’s a different step that could be used later to characterize the circuit’s behavior, but the standard first step to find V_th is open-circuit measurement.