Definition:SI/Power/Watt

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Definition

The watt is the SI unit of power.


It is defined as being the rate at which $1$ joule of energy is uniformly transformed in $1$ second:

$1 \, \mathrm W = 1 \, \mathrm J \, \mathrm s^{-1}$


Hence it can be understood as:

the rate at which work is done when the velocity of a body is held constant at $1$ metre per second against a constant opposing force of $1$ newton
the rate at which work is performed when an electric current of $1$ ampere flows across an electrical potential difference of $1$ volt.


Conversion Factors

\(\ds \) \(\) \(\ds 1\) watt
\(\ds \) \(=\) \(\ds 10^7\) ergs per second
\(\ds \) \(=\) \(\ds 0.2389\) $15 \cels$ calorie per second


Symbol

$\mathrm W$

The symbol for the watt is $\mathrm W$.


Its $\LaTeX$ code is \mathrm W .


Base Units

The SI base units of the watt are:

$\mathrm W := \mathrm {kg} \, \mathrm m^2 \mathrm s^{-3}$

where:

$\mathrm {kg}$ denotes kilograms
$\mathrm m$ denotes metres
$\mathrm s$ denotes seconds (of time).

This arises from the definition of the watt as $\mathrm J \, \mathrm s^{-1}$, that is, joules per second.


Source of Name

This entry was named for James Watt (I).


Sources

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