alleryStart learning →While going round a loop you cross a resistor in the same direction as the current flowing in it. What is the change in potential?
AA drop equal to I times R
BA rise equal to I times R
CA drop equal to the emf
DA rise equal to the emf
Answer & Solution
Correct answer: A. A drop equal to I times R
1. The sign convention for the loop rule is fixed by the direction of travel against the direction of current.
2. Crossing a resistor along the current gives a change of minus IR, a drop.
3. Crossing the same resistor against the current gives plus IR instead.
4. Emf terms follow a separate convention: plus emf when the crossing runs from minus to plus, and minus emf the other way.
5. Mixing the two conventions is the usual cause of a wrong sign in a loop equation.
_Source: OpenStax College Physics (CC BY 4.0), Ch 21 "Circuits and DC Instruments", section 21.3 Kirchhoff's Rules_
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