Source transformation principle: Is it impossible to convert between an ideal voltage source with series resistance and an equivalent current source with parallel resistance (and vice versa)?
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ATrue
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BFalse
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CTrue unless resistance is zero
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DTrue only for nonlinear loads
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ETrue for AC but not DC
Answer
Correct Answer: False
Explanation
Introduction / Context:Source transformations are a powerful analysis tool, allowing engineers to replace a Thevenin source with its Norton equivalent, simplifying circuit calculations without changing external terminal behavior.
Given Data / Assumptions:
- Thevenin form: ideal voltage source Vth in series with Rth.
- Norton form: ideal current source In in parallel with Rn.
- Equivalence is at the same two external terminals and for linear bilateral elements.
Concept / Approach:
The conversions are defined by In = Vth / Rth and Rn = Rth. Conversely, Vth = In * Rn. The two models produce the same open-circuit voltage, short-circuit current, and terminal V–I relation, ensuring equivalence.
Step-by-Step Solution:
Start with Vth in series with Rth.Compute the short-circuit current: Isc = Vth / Rth → define In = Isc.Retain the same resistance: Rn = Rth in parallel with In.Verify: Open-circuit voltage Voc = Vth = In * Rn; short-circuit current Isc = Vth / Rth = In.Verification / Alternative check:
Plot the terminal V–I characteristic; both models yield V = Vth − I * Rth = In * Rn − I * Rn, which are algebraically identical when Rn = Rth and In = Vth / Rth.
Why Other Options Are Wrong:
- Equivalence does not require zero resistance; it requires the stated relationships.
- Linearity is the key assumption; nonlinearity is not a requirement.
- The method applies to both DC and AC (using phasors/impedances).
Common Pitfalls:
Forgetting to keep the resistance the same in both forms, or mixing up open-circuit and short-circuit conditions when deriving In or Vth.
Final Answer:
False