Difficulty: Easy
Correct Answer: Zero internal resistance
Explanation:
Introduction / Context:Ideal sources are simplifying models used to reason about circuits. Knowing the defining property of an ideal voltage source helps predict how it behaves with any load and informs practical approximations in power supplies and instrumentation.
Given Data / Assumptions:
Concept / Approach:An ideal voltage source maintains a fixed terminal voltage regardless of load current. For that to be true in the Thevenin model, the internal resistance must be zero ohms so that no voltage drop occurs inside the source as current changes. This is the dual of an ideal current source, which has infinite internal resistance (Norton resistance).
Step-by-Step Solution:
1) Define ideal voltage source: Vout is constant for any load current.2) Model as Thevenin source: Vs in series with Rs.3) Require Rs = 0 Ω so Vout = Vs (no internal drop) for all currents.Verification / Alternative check:Using voltage division, Vout = Vs * RL / (Rs + RL). To keep Vout independent of RL, Rs must be 0, confirming the definition.
Why Other Options Are Wrong:
Infinite internal resistance: That describes an ideal current source.Load dependent voltage: Contradicts the definition of a voltage source.Load-dependent current: True in practice, but not the defining internal-resistance property.None of the above: Invalid since zero internal resistance is correct.Common Pitfalls:Confusing Thevenin and Norton duals; assuming nonzero internal resistance for “ideal” models.
Final Answer:Zero internal resistance.
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