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.
“The algebraic sum of changes in potential around any closed loop involving resistors and cells in the loop is zero.” What is this rule known as?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Loop rule
The passage gives Kirchhoff’s second law, the voltage law. It says that “the sum of all the voltages around a closed loop in any circuit must be equal to zero”. This is the loop rule. The passage adds that it is a consequence of the conservation of energy.
Option (1) Loop rule — Correct. Going once round a closed loop brings a charge back to its starting point. So the rises in potential across the cells and the drops across the resistors must add up to zero.
Option (2) Junction rule — Incorrect. The junction rule deals with currents. It says that the sum of the currents flowing into a junction equals the sum flowing out. It follows from the conservation of charge.
Option (3) Right-hand rule — Incorrect. A right-hand rule gives the direction of a magnetic field or a magnetic force. It says nothing about the potential changes round a circuit loop.