Learning path: Electricity

Your path

1. ForcesDirect prerequisite

   A push or pull interaction between two objects, capable of changing an object's velocity. Newton's three laws of motion describe how forces and motion relate: a body keeps its state of motion unless acted on by a net force (first law), net force equals mass times acceleration, F = ma (second law), and forces between two bodies are equal and opposite (third law).

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2. EnergyDirect prerequisite

   The capacity to do work, taking forms such as kinetic energy (associated with motion) and potential energy (associated with position or configuration, such as height in a gravitational field). The total energy of an isolated system is conserved: energy changes form but is never created or destroyed.

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3. ElectricityYour goal

   Electricity is the behaviour of electric charge, and an electric current is charge flowing round a complete circuit, measured in amperes. A battery's potential difference (voltage) pushes the current, resistance opposes it, and for many materials they are linked by Ohm's law, V = IR. Circuits transfer energy at a rate P = IV; resistors add in series and combine as reciprocals in parallel. Mains electricity can kill and is never used for experiments.

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Where to go next

Concepts that build directly on Electricity:

• Batteries: A battery stores energy chemically and releases it as electricity: in each cell, a chemical reaction pushes electrons out of the negative electrode (anode), through the circuit, and into the positive electrode (cathode). Single-use (primary) cells cannot be recharged; rechargeable (secondary) cells use reversible reactions. Lithium-ion cells, honoured by the 2019 Nobel Prize in Chemistry, power phones and laptops; because their lithium ions move in and out of the electrodes without consuming them, they can be recharged hundreds of times.
• Magnetism: Magnetism is the push and pull between magnets, and between moving charges, carried by a magnetic field measured in teslas. Every magnet has a north and a south pole that cannot be separated; like poles repel and unlike poles attract. Electric currents create magnetic fields, and changing magnetic fields create currents — the link that powers generators and, together with electricity, explains light.
• Semiconductors: Semiconductors such as silicon conduct electricity better than insulators but far less than metals, because only a small energy gap separates their filled and empty electron bands. Adding tiny amounts of impurity (doping) creates n-type material, rich in electrons, or p-type material, rich in holes. Joining the two makes diodes and transistors — the switches and amplifiers from which every computer chip is built.