Radioactive isotopes can be used as power sources for remote devices such as satellites. The radioactive source can be placed in a container which produces electricity as a result of absorbing heat. The source needs to have a high activity and a long half-life.A thermocouple is an electrical device made of two different metals joined together. At the junction a potential difference is produced if the metals are heated. If this is part of a complete circuit the potential difference will cause a current to flow. This is called a thermoelectric generator.