Finding Thevenin equivalent: to determine the Thevenin open-circuit voltage V_th seen at a pair of terminals, what should you do with the load connected to those terminals?

Introduction / Context:
Thevenin equivalents simplify complex linear circuits into a single voltage source V_th in series with a resistance R_th as seen from two terminals. The first step is to find V_th, the open-circuit voltage at those terminals. Knowing the correct measurement condition prevents errors when characterizing sources and interconnections.

Given Data / Assumptions:

• We are working with a linear circuit of independent/dependent sources and resistors.
• The load is externally connected to the terminals of interest.
• The goal is to find V_th, the open-circuit terminal voltage.

Concept / Approach:
By definition, V_th is the terminal voltage with no load attached, i.e., under open-circuit conditions so that load current is zero. Removing (opening) the load ensures that any voltage drop across internal Thevenin resistance is due only to internal network behavior, not to load current. Only after V_th is found do we compute R_th (by source deactivation or by measuring the short-circuit current and using R_th = V_th / I_sc).

Step-by-Step Solution:
Disconnect the load → open-circuit the terminals.Calculate or measure the resulting terminal voltage; this is V_th.Optionally, find I_sc by shorting the terminals and computing current, then get R_th = V_th / I_sc.Reattach the load to use the Thevenin model for analysis.

Verification / Alternative check:
Apply to a voltage divider: With the load removed, the divider’s output equals V_th. With the load attached, output droops because current flows through R_th, justifying the open-circuit condition when finding V_th.

Why Other Options Are Wrong:
Shorting the load (A) gives I_sc, not V_th. Options C and D describe source deactivation for R_th by the deactivation method, not for V_th. “None” is incorrect because opening the load is exactly right.

Common Pitfalls:
Forgetting dependent sources must remain active when finding R_th by test-source methods; mixing up V_th and I_sc measurement conditions.

Final Answer:
Open the load resistor