Unit 12
Electricity.
From rubbed charge to a capacitor: fields and potential, current and resistance, circuits, and semiconductors.
Before this unit
- Energy
- Linear equations Mathematics
The unit, lesson by lesson
Lessons
6 lessons · 32 practice questions · about 3 hours
Electric charge
Rubbing moves electrons: positive and negative charge, conservation of charge, counting the electrons in a charge, and why a charged balloon pulls on neutral paper.
Coulomb's law, field and potential
The force between two charges and how it falls with the square of the distance, the electric field as force per coulomb, fields that add as vectors, and potential: energy per coulomb.
Current, voltage and resistance
What flows in a wire, voltage as energy per coulomb, Ohm's law, why a battery does not give a fixed current, and the power a bulb takes.
Circuits in series and parallel
Three bulbs on a 12 V battery: the total resistance in series and in parallel, current that is not used up, voltage that is shared, and what happens to one bulb when its neighbour is switched off.
Capacitors
Two metal plates on a battery: equal and opposite charge on the plates, capacitance and what sets it, what an insulator between the plates changes, and the energy a capacitor stores.
Conductors, insulators and semiconductors
Why copper conducts, diamond does not, and silicon sits in between: energy bands and the gap between them, heat lifting electrons across the gap and leaving holes, and why a semiconductor conducts better when it is warm.