'NCEES FE Electrical and Computer Practice Exam 2025 – All-in-One Guide to Master Your Engineering Fundamentals!'

The formula for Thevenin or Norton equivalent resistance is derived based on the relationship between open-circuit voltage and short-circuit current. The correct option identifies this relationship by stating that the equivalent resistance can be calculated as the open-circuit voltage divided by the short-circuit current.

In a circuit, the open-circuit voltage is the voltage measured across the terminals when no load is connected, providing insight into the maximum voltage available from the source. On the other hand, the short-circuit current is the current flowing when the terminals are directly connected with a hypothetical wire, which helps to understand how much current the circuit can deliver under short-circuit conditions.

When you use the formula, you essentially obtain a measure of resistance that reflects how the circuit behaves under load variations, making it a foundational concept in circuit analysis. The use of voltage and current in this context aligns with Ohm's Law, reinforcing the understanding of how voltage, current, and resistance interact in electrical circuits.

This approach is crucial for simplifying complex circuits into manageable forms for analysis and design, which is the essence of both Thevenin’s and Norton’s theorems.