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NUE 052 - Power, Energy & Efficiency

Electrical Energy and Work
Electricity is produced by converting other forms of energy like heat or light. The supply company then distributes this energy to consumers over high voltage overhead wires. When close to the consumer the energy is changed to the low voltage supply available at a standard electrical socket. A unit of energy is known a joule. Energy is the ability to do work. It can be said that when energy is transformed from one form to another, work is done. Sunlight can generate electricity

Power is the rate that energy is used or work is done. The unit of power is the watt with a symbol of the letter W. The watt is named after James Watt the English inventor who was responsible for the term 'horsepower'. One horsepower is equal to 746 watts.

James Watt is responsible for the term Horsepower
All systems have losses which is power used in excess to the requirements of the load. These losses can be mechanical and/or electrical. Efficiency is expressed as a percentage of the ratio of power output to power input. The symbol is n (pronounced 'eta') expressed in a number followed by the percent symbol; e.g., efficiency = 89%
Formula for finding efficiency



 is done when energy is converted from one form to another, e.g. from sunlight to voltage


 is the rate of doing work


 is the ability to do work

Torque is the term used for for the effect of a force producing rotation about a a point. Torque can only be present when there is rotation.
The ability of an electric motor to turn a shaft is measured in torque.
Practice Tests Practice tests are available on the Practice Test page

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