Everything about Units Of Energy totally explained
Because
energy is defined via
work, the
SI unit for
energy is the same as the unit of work – the
joule (J), named in honour of
James Prescott Joule 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:
An energy unit that's used in
atomic physics,
particle physics and
high energy physics is the
electronvolt (eV). One eV is equivalent to
1.60217653×10−19 J. In
spectroscopy the unit cm
-1 = 0.0001239 eV is used to represent energy since energy is inversely proportional to wavelength from the equation
.
In discussions of energy production and consumption, the units
barrel of oil equivalent and
ton of oil equivalent are often used.
When discussing amounts of energy released in
explosions or
bolide impact events, the
TNT equivalent unit is often used. 1 ton of TNT equivalent is equal to 4.2 × 10
9 joules. Therefore, 1 kT TNT is 4.2 × 10
12 joules, and 1 MT TNT is 4.2 × 10
15 joules.
Note that
torque, the "rotational force" or "angular force" which causes a change in rotational motion is typically expressed in newton-metres. This isn't a simple coincidence: a torque of 1 newton-metre applied on 1 radian requires exactly 1 newton-metre = 1 joule of energy.
Other units of energy
In
cgs units, one
erg is 1
g cm2 s−2, equal to 1.0×10
−7 J.
The
imperial/
U.S. units for both energy and work include the
foot-pound force (1.3558 J), the
British thermal unit (Btu) which has various values in the region of 1055 J, and the
horsepower-hour (2.6845 MJ).
The energy unit used for everyday
electricity, particularly for utility bills, is the
kilowatt-hour (kWh), and one kWh is equivalent to 3.6×10
6 J (3600 kJ or 3.6 MJ). Electricity usage is often given in units of kilowatt-hours per year (kWh/yr). This is actually a measurement of
power consumption, for example, the rate at which energy is transferred.
The
calorie equals the amount of
thermal energy necessary to raise the
temperature of one
gram of
water by 1
Celsius degree, at a
pressure of 1
atm. For thermochemistry a calorie of 4.184 J is used, but other calories have also been defined, such as the International Steam Table calorie of 4.1868 J.
Food energy is measured in large calories or kilocalories, sometimes capitalized as "Calories" (= 10
3 small calories).
In physics, it's still common to measure energy on the atomic scale in the non-SI, but convenient, units
electronvolts (eV).
Conversion of units
For conversion of units of energy, see
Conversion of units#Energy, work, or heat.
Further Information
Get more info on 'Units Of Energy'.
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