Generating and using electricity

How a generator works

A generator transforms kinetic energy into electrical energy. Inside is a magnet and a coil of copper wire. When one of them spins, the magnetic field sweeping through the coil pushes electrons along the wire. Because the magnet's north and south poles take turns passing the coil, the current flows one way, then the other, many times a second. This is alternating current (AC). In Australia the mains supply changes direction 50 times each second (50 hertz).

You get more voltage from a generator by:

• spinning it faster;
• using more turns of wire in the coil;
• using a stronger magnet.

A motor is a generator run in reverse: electrical energy in, kinetic energy out. Electric cars use this cleverly. When the driver brakes, the motor works as a generator, turning the car's kinetic energy back into electrical energy to recharge the battery. This is called regenerative braking.

Power stations

Most power stations differ only in how they get the generator spinning.

• Coal and gas: burn fuel to boil water; high-pressure steam spins a turbine (a shaft with many angled blades) connected to the generator. Chemical → heat → kinetic → electrical.
• Hydroelectric: water from a dam falls through pipes and spins the turbine. Gravitational potential → kinetic → electrical. The Snowy Mountains Scheme was built mostly by migrant workers from over 30 countries between 1949 and 1974.
• Wind: moving air spins the blades. Kinetic → electrical.
• Solar panels are the odd one out: they have no moving parts and no generator. Light is transformed directly into electrical energy.

The electricity grid

The network of power lines that links power stations to homes and businesses is called the grid. Wires heat up when current flows through them, wasting energy. The bigger the current, the bigger the loss. To keep current low, electricity is sent long distances at very high voltage.

Transformers change the voltage of AC electricity. A step-up transformer at the power station raises the voltage to between 132 000 V and 500 000 V for the transmission lines. Substations step it down to 11 000 V for the streets, and transformers on poles or in green ground boxes step it down again to 230 V for homes. Transformers only work with AC, which is one big reason why the grid uses AC rather than DC.

Batteries and DC

A battery stores chemical potential energy and transforms it into electrical energy when it's connected in a circuit. Batteries give direct current (DC), which flows in one direction only. Phones, laptops and cars run on DC, so phone chargers include a circuit that converts the mains AC to low-voltage DC.

Single-use batteries (such as alkaline AA cells) can't be recharged. Rechargeable batteries can be run backwards: a charger pushes current into them, rebuilding the chemicals. Most phones, laptops, electric cars and home batteries use lithium-ion cells, which store a lot of energy for their mass. Damaged lithium batteries can overheat and catch fire, which is why they must never go in household bins. Take them to a battery recycling drop-off point instead.

Lighting and electronics

For over a century homes were lit by incandescent globes, which pass current through a thin tungsten filament until it glows white hot (about 2500 °C). Australia was the first country to announce a ban on them, in 2007, and they were phased out from 2009. Compact fluorescent lamps (CFLs) replaced them for a while, but these contain a little mercury. Today almost all new lights are LEDs (light-emitting diodes), which make light directly from electrical energy in a tiny piece of semiconductor, with much less heat.

LEDs are one kind of semiconductor device. Another, the transistor, was invented in 1947 and acts as a tiny electronic switch. Transistors made radios pocket-sized, and then engineers learned to build thousands, then millions, then billions of them onto one small chip of silicon: an integrated circuit. A modern phone processor contains more than 15 billion transistors, each far smaller than a virus.