Node law — current conservation: At a junction (node) in an electrical network, is it possible for the total current entering the node to differ from the total current leaving the node under normal steady conditions?
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ACorrect
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BIncorrect
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CTrue only during capacitor charging
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DTrue only at very high frequency
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ETrue if the meter accuracy is low
Answer
Correct Answer: Incorrect
Explanation
Introduction / Context:Kirchhoff’s Current Law (KCL) states that the algebraic sum of currents entering and leaving a node is zero. This embodies conservation of charge and is fundamental to circuit analysis across DC and AC regimes for lumped networks.
Given Data / Assumptions:
- Ideal lumped-element circuit model.
- Steady conditions or sinusoidal steady state for AC.
- No charge accumulation at an ideal node.
Concept / Approach:KCL arises because charge cannot pile up indefinitely at a point in a lumped model; any current arriving must depart. Mathematically, sum(I_in) = sum(I_out). Transient elements like capacitors are handled by defining branch currents consistently; KCL still holds at every instant when displacement currents are included in Maxwell-consistent models.
Step-by-Step Solution:
1) Define the node and enumerate incident branch currents with a sign convention. 2) Apply conservation of charge: net inflow equals net outflow. 3) Conclude that entering current cannot differ from leaving current in the model. 4) Use KCL to solve for unknown currents in parallel networks.Verification / Alternative check:Simulations and nodal analysis rely on KCL; measured discrepancies typically result from instrument error or parasitic storage, not a violation of the law itself within the lumped model assumptions.
Why Other Options Are Wrong:
- Correct: The statement is not correct; KCL forbids a mismatch.
- True only during capacitor charging: KCL still holds when capacitor branch current is included.
- True only at very high frequency: KCL holds; modeling may require displacement current but conservation remains.
- True if the meter accuracy is low: Measurement error does not change physical laws.
Common Pitfalls:Interpreting meter mismatch as a physical violation; overlooking displacement currents in high-frequency or field-theory contexts and then misapplying the lumped model.
Final Answer:Incorrect