Case: Read the passage and answer the question.
Kirchhoff’s first law applies to currents at a junction in a circuit. It states that at a junction in an electrical circuit, the sum of the currents flowing into the junction is equal to the sum of the currents flowing out of the junction. Kirchhoff’s second law, also known as Kirchhoff’s voltage law, states that the sum of all the voltages around a closed loop in any circuit must be equal to zero. The first law is a consequence of the conservation of charge, and the second law is a consequence of the conservation of energy. The Wheatstone bridge, also known as the resistance bridge, finds an unknown resistance by balancing two legs of the bridge circuit and works on Kirchhoff’s laws.
Consider the following statements about Kirchhoff’s rules:
(A) The junction rule holds at any point on a single wire as well as at a junction of several wires.
(B) If a current marked with an arrow comes out negative, the actual current flows opposite to the arrow.
(C) At a junction, the currents add up by the law of vector addition.
(D) Bending a wire at a junction makes the junction rule invalid.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) and (B) only
Kirchhoff’s rules help to find the currents in circuits that cannot be split into simple series and parallel parts. Each current is first given a symbol and an arrow.
(A) The junction rule holds at any point on a single wire as well as at a junction of several wires. — True. Charge does not pile up anywhere in a steady current. So the current going into any point of a wire equals the current coming out.
(B) If a current marked with an arrow comes out negative, the actual current flows opposite to the arrow. — True. The arrow is only a guess of the direction. A negative answer means the current flows the other way.
(C) At a junction, the currents add up by the law of vector addition. — False. Current is a scalar. The arrow only shows the sense of flow, so the currents at a junction add as ordinary numbers.
(D) Bending a wire at a junction makes the junction rule invalid. — False. The junction rule comes from the conservation of charge. Bending or turning a wire does not change the charge flowing in and out.
NCERT (2026-27):
Kirchhoff’s Rules – “This applies equally well if instead of a junction of several lines, we consider a point in a line.”
Kirchhoff’s Rules – “… If I turns out to be negative, the current actually flows in a direction opposite to the arrow. …”
Points to Ponder – “Currents do not obey the law of vector addition. …”
Points to Ponder – “… Bending or reorienting the wire does not change the validity of Kirchhoff’s junction rule.”