Physics · The particulate nature of matter. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Current is the rate of flow of charge. The emf of a cell is the energy it gives to each coulomb of charge. Potential difference is the energy each coulomb transfers in a component. Resistance is the ratio V/I. It is constant for an ohmic conductor, but it rises in a filament lamp as the lamp gets hotter.
Two conservation laws solve every circuit. Charge is conserved, so the current into a junction equals the current out. Energy is conserved, so round any loop the emfs equal the sum of the potential differences.
A real cell has internal resistance, so some volts are lost inside it and the terminal potential difference falls when the current rises. A potential divider shares the supply voltage in the ratio of the resistances.
Students forget to convert units in the resistivity equation. An area in mm2 must be multiplied by 10−6 to give m2, and doubling the diameter makes the area four times larger, not two.
Answer: About 5.6 W in each resistor.
Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.