Conservation of charge at circuit junctions

Steps:

• Recall Kirchhoff's second law as the current law (KCL), stating algebraic sum of currents at a junction is zero.
• Link it to the basic principle that electric charge is conserved in steady-state circuits, preventing accumulation at points.
• Express this principle mathematically: sum of currents entering a junction equals sum leaving it.
• Match the description to option B, confirming it as the foundational principle.

Why B is correct:

• KCL follows from charge conservation, formulated as ∑I_in = ∑I_out at any junction (from continuity equation in electromagnetism).

Why the others are wrong:

• A: States energy conservation, which underlies Kirchhoff's voltage law (KVL), not the current law.
• C: Not enough information (option blank).
• D: Describes KVL application via Ohm's law (∑V = ∑IR), not charge conservation.

Final answer: B