Energy can be neither created nor destroyed, but it can be changed from one form to another. Electrical energy is most commonly generated by rapidly rotating an electrical conductor in a magnetic field, thereby inducing an electric current in the conductor by converting mechanical energy to electrical energy. The source of the mechanical energy to rotate the conductor is often steam spinning a turbine, the heat to vaporize water being supplied by burning a fossil fuel, from the decay of radioactive fuel in a nuclear reactor, or potentially from the fusion of atoms in a thermonuclear reactor. Alternatively, the kinetic energy of wind or flowing water can be used to spin a turbine. Electricity is also produced by converting light (electromagnetic radiation) directly into electricity through the photovoltaic effect, or using sunlight to supply the heat to raise steam.