Question

Kirchhoff’s first law i.e., $\sum i=0$ at a junction is based on the law of conservation of
(A) Charge
(B) Energy
(C) Momentum
(D) Angular momentum

Answer 1

Hint Kirchhoff’s first law, which is the junction rule, states that the charge entering a junction/node is the same as the charge leaving the junction/node in an electrical circuit. This is only possible when charges can neither be created nor be destroyed.

Complete Step-by-step solution
The law of conservation of charge states that the charge can’t be created and also it can’t be destroyed.
So as the charge is conserved, the charge entering a node and leaving the node will be the same which is the statement of Kirchhoff’s junction law.
Kirchhoff’s first law i.e. junction rule is centered on the law of conservation of charge.

Therefore the correct answer to the above question is (A) Charge.

Additional information
Other options were incorrect as the conservation of other quantities was not appropriate towards validating Kirchhoff’s first rule.
The Law of Conservation of Energy states that energy can neither be created and even it can’t be destroyed but it can be converted from one sort of energy to another.
The Law of conservation of momentum states that the momentum of a body remains constant unless and until an external unbalanced force is applied.
The Law of conservation of angular momentum states that the angular momentum of a body remains constant unless and until an external unbalanced torque is applied.

Note
There is another Kirchhoff’s law which is known as the loop law which is based on conservation of energy which states that the sum of potential difference across all the appliances in a closed circuital loop is zero. Also, these laws are only applicable when there is no induced potential difference in the circuit.