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Definition - What does Joule mean?

Joule is a standard unit of measurement for work or energy used in electricity, mechanics, thermal energy and general scientific applications. The unit is named in recognition of British physicist James P. Joule. Like all SI units, the letter of its symbol is written in upper case, yet is in lowercase when it is spelled out in English.

Techopedia explains Joule

A joule is defined as the amount of energy transferred to an object when a force of one newton acts on the object in the direction of its motion through a distance of one meter (1 newton meter or Nm). It can also be defined as energy dissipated as heat when an electric current of one ampere passes through a resistance of an ohm for one second. It is also equal to one watt of power emitted or dissipated for one second, or watt second (Ws).

In various applications, British thermal units (BTU) are used to express the unit for energy. One BTU is equal to approximately 1,055 joules.

One joule is equal to:

  • 1 × 107 erg (exactly)
  • 6.24150974 × 1018 eV
  • 0.2390 cal (gram calories)
  • 2.390 × 10-4 kcal (food calories)
  • 9.4782 × 10-4 BTU

Units defined exactly in terms of the joule include:

  • 1 thermochemicalcalorie = 4.184 J
  • 1 international tablecalorie = 4.1868 J
  • 1 watt hour = 3,600 J (or 3.6 kJ)
  • 1 kilowatt hour = 3.6 × 106 J (or 3.6 MJ)
  • 1 watt second = 1 J
  • 1 ton TNT = 4.184 GJ
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