The Watt is a unit of power.

The term comes from the name of the engineer James Watt who contributed to the development of the Steam engine.

Definition

The Watt (symbol W ) is the unit IF of power, radiant Energy flux and thermal Flux.

One Watt is the power of an energy system in which is uniformly transferred a energy from 1 joule during 1 second:

$$

W = J \ cdot s^ {- 1} = NR \ cdot m \ cdot s^ {- 1} = kg \ cdot m^2 \ cdot s^ {- 3}

or:

$1\; \backslash \; \backslash \; mathrm\; \{W\}\; =\; 1\; \backslash \; \backslash \; dfrac\; \{\backslash \; mathrm\; \{J\}\}\; \{\backslash \; mathrm\; \{S\}\}\; =\; 1\; \backslash \; dfrac\; \{\backslash \; mathrm\; \{NR\; \backslash \; cdot\; m\}\}\; \{\backslash \; mathrm\; \{S\}\}\; =\; 1\; \backslash \; \backslash \; dfrac\; \{\backslash \; mathrm\; \{kg\}\; \backslash \; cdot\; \backslash \; mathrm\; \{m^2\}\}\; \{\backslash \; mathrm\; \{s^3\}\}$

In electricity

In electricity, Watt is the power of a system outputting a intensity of 1 amp under a tension of 1 Volt. It is the product of the tension by the intensity:

$P\; (T)\; =\; U\; (T)\; \backslash \; cdot\; I\; (T)$

$P\; (T)$ - power according to $t$ - (Watt).

$U\; (T)$ - electric Tension according to $t$ - (Volt).

$I\; (T)$ - Electric current according to $t$ - (Amp).

It can be a question of an average, effective or instantaneous power, according to the nature of the currents and the tensions (continuous or alternate) and of their variation according to time.

In integral this power over a time of 1 hour, one obtains a quantity of energy of which the unit current practice is the Kilowatt-heure equivalent with 3600000 joules.

The megawatt (MW) - that is to say a million Watts - is a unit frequently used in electric production, a section of French Nuclear plant (which includes/understands four in general of them) generally delivers a power of 1300 MW electric. The gigawatt (GW) corresponds, him, to a billion Watts.

The térawatt (TW) - that is to say one 10 Watts - is used for comprehensive assessments of powers.

In mechanics

In Mécanique Watt is the power of a system providing a work of 1 newton on a distance from 1 Mètre during 1 second. If the point of application of a force of 1 Newton moves at the speed of 1 m/s the power is worth 1 Watt:

$P\; =\; \backslash \; frac\; \{F\; S\}\; \{T\}\; =\; \backslash \; int\; F\; \backslash \; cdot\; \backslash \; mathrm\; \{D\}\; v\; =\; \backslash \; frac\; \{\backslash \; mathrm\; \{D\}\; W\}\; \{\backslash \; mathrm\; \{D\}\; T\}$

$F$ - force - (newton).

$s$ - distance - (Meter).

$t$ - time - (second).

$v$ - Speed - (m/s).

$W$ - work - (Joule).

Orders of magnitude

With the image of the acceleration which should not be confused with the concept speed, the concept of power (measured in Watt) should not be confused with the concept of energy (measured in joule). Power being the quotient of energy by time.

Thus, if a work of 600 J must be produced (corresponding for example to energy required to raise the temperature of water glass of 100 ml of 18,5 °C with 20 °C), it will be carried out for example:

• in 10 minutes (that is to say 600 seconds) with a machine of a power of 1 W (in practice: apparatus in mode “takes care”);
• in 1 minute (that is to say 60 seconds) with a machine of a power of 10 W (in practice: power of a small electric bulb);
• in 1 second with a machine of a power of 600 W (in practice: power of an electric drilling machine).

Watt can be regarded as a small unit. For memory:

• a town car of 100 CH delivers a power of 73600 W (i.e. 73,6 kw);
• a professional racing cyclist can deliver with full effort, and over a short moment, a power of 1.500 W (i.e. 1,5 kw);
• a washing machine the linen requires a power of about 1.000 to 2.000 W;
• a fixed desktop machine with its screen LCD approximately consumes a power from 150 to 200 W;
• a current electric bulb with incandescence requires a power of 60 W (5 times less for a fluorescent Lampe with electronic ballast known as “low consumption”).

Electric and thermal Watt

The electric Watt (abbreviation: We) corresponds to the production of electric output. Its multiples are the electric megawatt (MWe) and the electric gigawatt (GWe).

The thermal Watt (abbreviation: Wt or Wth) corresponds to the heat production. Its multiples are the thermal megawatt (MWt or MWth) and the thermal gigawatt (GWt or GWth).

This precision is necessary to distinguish the electric production from the thermal production of a power station. For example, the nuclear plant of Embalse in Argentina generates 2109 MW of heat (2109 MWth), and only 648 MW of electricity (648 MWe), since the thermal energy conversion into electrical energy can be done only with losses (effectiveness of about 30 to 40%).

See too

Internal bonds

• Power
• Order of magnitude (power)
• Diagram of Watt
• Tariff of electricity
• Kilowatt-hour
• Watt-peak

External bonds

• Definition of Watt on energy-environnement.ch

• Conversion of Watt towards other units of power

Simple: Watt Zh-min-nan: Oá

Random links:

Disease of Niemann-Pick | Echoendoscopy | Hippolyte Bernheim | Antoine Richard | Cycle of Fulgur