Chemical cells (commonly called batteries)
A common source of electric charge is the torch battery. Strictly, a torch battery should be called a dry cell, not a battery. A battery is made up of a group of cells working together.
A torch battery contains a paste of chemicals, and is said to be a dry cell since it does not contain a liquid.
A common dry cell used in torches consists of a rod surrounded by a chemical paste in a metal case.
The chemicals in the paste keep taking electrons from the rod and giving them to the case. Electrons have a negative electric charge. Hence, there is a build-up of negative charge on the case. The rod becomes positive because it has lost negative electrons.
When the wires of the circuit are connected, the electrons can flow from the negative case through the circuit to the rod. Hence, there is a continuous current flow.
There are other dry cells besides the carbon/zinc cells. There are the alkaline cells, mercury and lithium cells. These are more expensive than carbon/zinc cells, but they supply a better source of electric charges.
Most of the electricity produced for households by the power stations comes from large generators. A generator uses magnetism to create electricity.
Certain crystals produce electricity when squeezed or stretched. Many gas barbecues are ignited using the piezoelectric effect. When the ignition knob is pushed or turned quickly, it squeezes a crystal that produces an electric spark that lights the gas for the barbecue.
Solar panels generate electricity from light energy. Some calculators are powered by solar cells. In parts of Australia some telephones are powered by solar cells, as shown.