Definition check: In Thevenin’s theorem, the Thevenin equivalent voltage seen at two terminals equals which measurable quantity of the original network?

Introduction / Context:
Thevenin’s theorem allows any linear two-terminal network to be represented by a single ideal voltage source in series with an equivalent impedance. Correctly identifying the Thevenin voltage, V_TH, is essential to build this model and to predict how different loads will behave when connected across the terminals.

Given Data / Assumptions:

• We are analyzing a linear, bilateral circuit in steady state.
• No load is connected while determining V_TH.
• Measurements are made at the two terminals of interest.

Concept / Approach:
The Thevenin equivalent voltage, V_TH, is by definition the terminal voltage with the load removed, i.e., the open-circuit voltage V_OC. With no load, there is no current through the external terminals; internal source and network interactions fix the terminal potential, which becomes V_TH. Once V_TH is known and Z_TH computed, any load response follows from simple voltage division in the Thevenin model.

Step-by-Step Solution:

Verification / Alternative check:
Connect a test load Z_L and predict the load voltage using the Thevenin model: V_L = V_TH * Z_L / (Z_TH + Z_L). If you instead compute V_L directly on the original network, results will match, confirming that V_TH was correctly identified as V_OC.

Why Other Options Are Wrong:

• 'equal to the source voltage': Internal drops may make the terminal voltage differ from the source value; only in trivial cases are they equal.
• 'the same as the load voltage': Load voltage depends on Z_L and is not defined for the open-circuit condition.
• 'none of the above': Incorrect because V_TH explicitly equals the open-circuit terminal voltage.

Common Pitfalls:

• Confusing V_TH with the internal source value instead of the measurable terminal voltage without load.
• Attempting to find V_TH with the load still connected.

Final Answer:
the open circuit voltage