Electricity is all about creating a potential. A potential difference(voltage) between two points in a circuit of conductive material (i.e. wire) will cause movement of electrons in the material. Electrons have a negative charge so they move towards the more positive potential. The movement of electrons is electricity and the rate at which the electrons move is current. For historical reasons¹, and to cause as much confusion as possible to anyone studying electronics, conventional current is in the opposite direction to the motion of the electrons.

Batteries

Batteries give a constant potential difference when included in a circuit. There are many different types and sizes of battery which provide a variety of voltages. Conventional batteries eventually (or quickly) stop working as they have limited power. Rechargeable batteries come in similar sizes to conventional batteries but can be recharged.

Lemon Power

Anyone can make a simple battery using just a lemon and two different pieces of metal. Of course, in order to see it work you also need some wires and a small (low resistance) light bulb. Simply stick the two bits of metal - say an iron nail and a piece of copper wire - into the lemon at different points (so the metals are not touching) and attach the light bulb to complete the circuit.

The potential difference is caused by the different metals and the lemon juice allows ions (charged particles) to move between the two. The metals have to be different for this to work and depending on what combination is used, the bulb may be brighter or duller.

Solar Cells

Solar Cells use energy from the sun to create a potential. They are made from two layers of silicon based material which have slightly different properties. When the sun shines on the solar cell, one layer becomes electro-postitive and the other electro-negative so there is a potential difference which can be used to power a circuit. Small solar cells are often found on calculators which require only a small voltage. Bigger solar cells can provide larger voltages and so power water heaters, satellites and special cars.