Kirchhoff's First Law (Current Conservation at Junctions)

Steps:

• Kirchhoff's first law states that the total current entering a junction equals the total current leaving it.
• In the circuit, I1 and I2 represent currents at a junction with no other branches indicated.
• For charge conservation, the equation must balance these currents directly.
• Option A equates I1 and I2, satisfying the law.

Why A is correct:

• It directly applies the junction rule, where sum of currents into a node is zero, so I1 entering equals I2 leaving.

Why the others are wrong:

• B: Introduces undefined current Is, violating the law's requirement for all currents at the junction.
• C: Relates voltages summing to zero, which is Kirchhoff's second law (loop rule), not the first.
• D: Equates voltages, irrelevant to current conservation in the first law.

Final answer: A