Energy
Energy exists in many forms, such as potential, kinetic, thermal, electrical, chemical, and nuclear energy. It can neither be created nor destroyed, but only transformed from one form to another. This principle is known as the law of conservation of energy, or the first law of thermodynamics.
Energy can be converted from one form to another in various ways, for example by burning wood or oil—which converts chemical energy into heat—or by using the potential energy stored in a reservoir behind a dam, which is converted into kinetic energy when the water flows through the dam to turn a turbine.
Solar energy is produced by nuclear fusion occurring in the Sun. This energy can be converted into electricity using solar cells (photovoltaic cells). In these cells, a small electrical voltage is generated when light strikes the junction between a metal and a semiconductor (such as silicon), or between two different semiconductors.
Unit Conversion