Watt

The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor of James Watt (1736–1819), an 18th-century Scottish inventor, mechanical engineer, and chemist who in 1776 improved the Newcomen engine with his own steam engine, which became fundamental for the Industrial Revolution.

Overview

When an object's velocity is held constant at one meter per second against a constant opposing force of one newton, the rate at which work is done is one watt.

1

W

=

1

J

/

s

=

1

N

⋅

m

/

s

=

1

k

g

⋅

m

2

⋅

s

−

3

.

{\displaystyle \mathrm {1~W=1~J{/}s=1~N{\cdot }m{/}s=1~kg{\cdot }m^{2}{\cdot }s^{-3}} .}

In terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V), meaning the watt is equivalent to the volt-ampere (the latter unit, however, is used for a different quantity from the real power of an electrical circuit).

1

W

=

1

V

⋅

A

.

{\displaystyle \mathrm {1~W=1~V{\cdot }A} .}

Two additional unit conversions for watt can be found using the above equation and Ohm's law.

1

W

=

1

V

2

/

Ω

=

1

A

2

⋅

Ω

,

{\displaystyle \mathrm {1~W=1~V^{2}/\Omega =1~A^{2}{\cdot }\Omega } ,}

where ohm (

Ω

{\displaystyle \Omega }

) is the SI derived unit of electrical resistance.

Examples

A person having a mass of 100 kg who climbs a 3-meter-high ladder in 5 seconds is doing work at a rate of about 600 watts.