Contains the full lesson along with a supporting toolkit, including teachers’ notes.
Over the past fifty years the capability of computers (often called 'computing power') has increased dramatically while the physical size and electrical power requirements have decreased.
The lesson examines the factors that determine energy use in computers and the steps that can be taken to minimise energy loss and extend battery life.
The invention of the electric battery in 1800 made it possible to produce a steady electric current and many people began intensive study of its effects. The heating effect was quickly noted; wires carrying large electric currents could even melt. The chemical effect was also discovered and applied in electrolysis andelectroplating (1800). In 1820, while demonstrating the heating effect of an electric current, the Danish scientist Hans Christian Ørsted (Oersted) discovered that an electric current had amagnetic effect.
Metals are generally good conductors of electricity; silver is the best followed closely by copper. However, all metals show someresistance to electric current and this gives rise to the heating effect. The resistance of a wire depends on the material, the length of the wire and its crosssectional area; long thinconductors have greater resistance than short thick ones. In 1849 James Joule discovered that the rate at which heat is produced, (i.e. the 'power') is proportional to the square of the current; this can be expressed concisely by the equation P=I2R, where P is the power, I is the current and R is the resistance.
The components in computers and other electronic devices are generally mounted on a 'printed circuit board' or PCB; the board is a non-conductor but metal tracks (usually of copper) are included to link the various components together. Reducing the size of computers involves reducing the width of the conducting tracks and thereby increasing their resistance. In practice energy losses due to track resistance are small compared with the losses in active components such as transistors and the integrated circuits (ICs or 'chips') that contain them.