Chapter 3 of 10All chapters
Chapter 3 of 10
Resistance and Ohm law
The relationship that solves most problems.
The law
Voltage equals current times resistance. Given any two, you have the third, and most circuit questions are that rearrangement plus care with units.
- Resistance rises with length and falls with cross-sectional area.
- Most metals gain resistance as they heat up.
Where energy goes
Current through a resistance produces heat. That is a fault in a cable, a feature in a kettle, and the reason thin wire on a high current is dangerous.