Electricity

The product of voltage and current equals electrical power. The unit of electrical power is the watt, named for James Watt. One watt of electrical power equals 1 joule per second. If 1 volt forces a 1-ampere current through a 1-ohm resistance, 1 joule per second will be wasted as heat. That is, 1 watt of power will be dissipated. A 100-watt incandescent lamp requires 100 joules for each second it operates.

Electricity provides a convenient way to connect cities with distant electrical generating stations. Electricity is not the primary source of energy, rather it serves as the means to transport energy from the source to a load. Electrical energy usually begins as mechanical energy before its conversion to electrical energy. At the load end of the distribution system the electrical energy is changed to another form of energy, as needed.

Commercial electrical power is transported great distances through wires, which always have significant resistance. Some of the transported energy is unavoidably wasted as heat. These losses are minimized by using very high voltage at a lower current, with the product of voltage and current still equal to the power required. Since the energy loss increases as the square of the current, a reduction of current by a factor of 1/100 reduces the power loss by a factor of 1/10,000. Voltage as high as 1,000,000 volts is used to reduce losses. Higher voltage demands bigger insulators and taller transmission towers, but the added expense pays off in greatly-reduced energy loss.