Joule

Joule is a unit of energy in the International System of Units. It is equal to the energy transferred to an object when a force of one newton acts on that object in the direction of the force's motion through a distance of one metre. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule.

Definition

The joule is named after James Prescott Joule. As with every International System of Units (SI) unit named for a person, its symbol starts with an upper case letter (J), but when written in full it follows the rules for capitalisation of a common noun; i.e., "joule" becomes capitalised at the beginning of a sentence and in titles, but is otherwise in lower case.

Practical examples

One joule in everyday life represents approximately:

• The energy required to lift a small apple (102 g) vertically through one metre of air.
• The heat required to raise the temperature of 1 g of water by 0.24 K.
• The amount of electricity required to light a 1 W LED for 1 s.

Multiples

For additional examples, see Orders of magnitude (energy).

Conversions

One joule is the equivalent of one watt of power radiated or dissipated for one second.

In terms of scientific units, one joule is approximately:

• 6.242×10^18 eV (electronvolts)
• 0.239 cal (calories, or "small calories")
• 0.000948 BTU (British thermal units)

See also

• Conversion of units of energy
• Orders of magnitude (energy)
• James Prescott Joule

External links

• What is a joule?

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