Kirchhoff's First Law, \( \sum I = 0 \) at a junction deals with conservation of:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Charge
Kirchhoff's first law (junction rule) says that the algebraic sum of the currents meeting at a junction is zero: the current flowing in equals the current flowing out.
\( \displaystyle \sum I = 0 \)
A current is the rate of flow of charge. Charge cannot pile up at a junction, nor can it be created or destroyed there, so whatever charge arrives per second must leave per second. The junction rule is therefore a statement of conservation of charge.
Option (1) Charge — Correct. The junction rule follows from the fact that charge does not accumulate at a junction.
Option (2) Energy — Incorrect. Conservation of energy is the basis of Kirchhoff's second law (loop rule), \( \sum \Delta V = 0 \) round a closed loop.
Option (3) Momentum — Incorrect. Momentum does not enter either of Kirchhoff's rules.
Option (4) Angular Momentum — Incorrect. Angular momentum has no role in circuit laws.
NCERT (2026-27):
Kirchhoff’s Rules – “… (a) Junction rule: At any junction, the sum of the currents entering the junction is equal to the sum of currents leaving the junction ….”
Kirchhoff’s Rules – “… The proof of this rule follows from the fact that when currents are steady, there is no accumulation of charges at any junction or at any point in a line.”