Q.Kirchhoff's first law, i.e., \sum I = 0 at a junction, deals with the conservation of (A) charge (B) energy (C) momentum (D) mass

Kirchhoff's Laws and Circuit Analysis

Complex circuits that cannot be reduced to simple series–parallel combinations are solved with Kirchhoff's two rules:

• Junction (current) rule — the algebraic sum of currents meeting at a node is zero, $\sum I = 0$. It expresses conservation of charge.
• Loop (voltage) rule — around any closed loop the algebraic sum of EMFs and $IR$ drops is zero, $\sum \varepsilon = \sum IR$. It expresses conservation of energy.

To apply them, assign a current to each branch, write one junction equation per independent node and one loop equation per independent mesh, and solve the simultaneous equations; a negative answer simply means the assumed direction was reversed. Where node potentials are given, the current in a branch follows directly from Ohm's law, $I=(V_1-V_2)/R$, and the junction rule fixes an unknown branch current from the others.

These laws handle multi‑cell networks (cells aiding or opposing), unbalanced bridges, and questions such as 'the current through a resistor is unchanged when an extra cell is added', which reduce to setting up and solving the loop and junction equations.

Kirchhoff's junction and loop rules are a core, high-weightage part of the CBSE Class 12 Physics Current Electricity chapter, frequently searched as "Kirchhoff's laws class 12 physics important questions" or "Kirchhoff's current and voltage law examples". Solving multi-loop and multi-cell networks with these rules is one of the most heavily tested numerical skills in board exams as well as JEE Main and NEET.