Units of energy

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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

${\displaystyle 1\ \mathrm {J} =1\ \mathrm {kg} \left({\frac {\mathrm {m} }{\mathrm {s} }}\right)^{2}=1\ {\frac {\mathrm {kg} \cdot \mathrm {m} ^{2}}{\mathrm {s} ^{2}}}}$

An energy unit that is used in atomic physics, particle physics and high energy physics is the electronvolt (eV). One eV is equivalent to 1.602176634×10⁻¹⁹ J.^[2]

In spectroscopy the unit cm⁻¹ ≈ 0.0001239842 eV is used to represent energy since energy is inversely proportional to wavelength from the equation ${\displaystyle E=h\nu =hc/\lambda }$.

In discussions of energy production and consumption, the units barrel of oil equivalent and ton of oil equivalent are often used.