Electricity from First Principles
Resistance & Ohm's Law
12 min · 2 worked examples · 3 questionsFree
What resistance physically is, and the one equation that ties it all together.
After this lesson you can
- Use V = I x R in any of its three forms
- Say what makes a wire's resistance high or low
- Recognise a component that does not obey Ohm's law, and why that matters
What resistance really is
As electrons drift through a conductor they collide with the vibrating atoms of the metal lattice. Each collision transfers a little energy to the lattice, which shows up as heat. That opposition to flow is resistance, measured in ohms (Ω).
This explains something you can feel: components get warm. The energy does not disappear, it becomes thermal energy. It also explains why resistance usually rises with temperature in metals, hotter atoms vibrate more vigorously, so there are more collisions.
In the full lesson
- What resistance really is
- What determines resistance
- Ohm's law
- Using it in practice
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.