Source modeling: Does a practical (real-world) voltage source always include a nonzero internal resistance when represented for circuit analysis?

Introduction / Context:
No physical source can maintain an absolutely constant terminal voltage under all loads. To capture real behavior (voltage sag and power loss), practical voltage sources are modeled with a series internal resistance.

Given Data / Assumptions:

• Practical voltage source with finite energy and non-ideal regulation.
• Internal resistance Rs is small but nonzero.
• Load connected across the source terminals.

Concept / Approach:

The Thevenin model represents a practical voltage source as an ideal source Vs in series with an internal resistance Rs. Under load, the terminal voltage drops: V_terminal = Vs − I_load * Rs. This explains regulation limits and heat dissipation inside the source.

Step-by-Step Solution:

Verification / Alternative check:

Measure open-circuit voltage (no load) and then loaded voltage. The drop from open-circuit to loaded conditions implies a finite internal resistance that can be estimated by Rs ≈ (V_oc − V_load) / I_load.

Why Other Options Are Wrong:

• Regulated supplies approximate low Rs but never exactly zero.
• Both AC and DC sources exhibit non-idealities; the model applies broadly.
• Internal resistance exists across operating currents, not only at high load.

Common Pitfalls:

Assuming data-sheet “tight regulation” implies zero Rs. It only means Rs is small over a specified load range.

Final Answer:

True