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Energy is defined via work, so the SI unit of energy is the same as the unit of work – the joule (J), named in honour of James Prescott Joule [1] and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units
This is the definition declared in the modern International System of Units in 1960. [13] The definition of the joule as J = kg⋅m 2 ⋅s −2 has remained unchanged since 1946, but the joule as a derived unit has inherited changes in the definitions of the second (in 1960 and 1967), the metre (in 1983) and the kilogram . [14]
However energy can also be expressed in many other units not part of the SI, such as ergs, calories, British thermal units, kilowatt-hours and kilocalories, which require a conversion factor when expressed in SI units. The SI unit of power, defined as energy per unit of time, is the watt, which is a joule per second. Thus, one joule is one watt ...
The kilowatt-hour is a composite unit of energy equal to one kilowatt (kW) sustained for (multiplied by) one hour. The International System of Units (SI) unit of energy meanwhile is the joule (symbol J). Because a watt is by definition one joule per second, and because there are 3,600 seconds in an hour, one kWh equals 3,600 kilojoules or 3.6 ...
Power is the rate at which energy is generated or consumed and hence is measured in units (e.g. watts) that represent energy per unit time. For example, when a light bulb with a power rating of 100 W is turned on for one hour, the energy used is 100 watt hours (W·h), 0.1 kilowatt hour, or 360 kJ. This same amount of energy would light a 40 ...
The erg is a unit of energy equal to 10 −7 joules (100 nJ). It is not an SI unit, instead originating from the centimetre–gram–second system of units (CGS). Its name is derived from ergon (ἔργον), a Greek word meaning 'work' or 'task'. [1] An erg is the amount of work done by a force of one dyne exerted for a distance of one centimetre.
The SI unit of electric potential energy is joule (named after the English physicist James Prescott Joule). In the CGS system the erg is the unit of energy, being equal to 10 −7 Joules. Also electronvolts may be used, 1 eV = 1.602×10 −19 Joules.
Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density , which is not to be confused with energy density , which is defined as energy per unit volume.