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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⋅m 2 ⋅s −3. [1] [2] [3] It is used to quantify the rate of energy transfer.
[a] In the SI system, it has units watts per square metre (W/m 2), or kg⋅s −3 in base units. Intensity is used most frequently with waves such as acoustic waves ( sound ), matter waves such as electrons in electron microscopes , and electromagnetic waves such as light or radio waves , in which case the average power transfer over one period ...
In physics and chemistry, it is common to measure energy on the atomic scale in the non-SI, but convenient, units electronvolts (eV). 1 eV is equivalent to the kinetic energy acquired by an electron in passing through a potential difference of 1 volt in a vacuum. It is common to use the SI magnitude prefixes (e.g. milli-, mega- etc) with ...
The SI has special names for 22 of these coherent derived units (for example, hertz, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (m 2), the SI derived unit of area; and the kilogram per cubic metre (kg/m 3 or kg⋅m −3), the SI derived unit of density.
The watt-second is the energy equivalent to the power of one watt sustained for one second. While the watt-second is equivalent to the joule in both units and meaning, there are some contexts in which the term "watt-second" is used instead of "joule", such as in the rating of photographic electronic flash units. [35]
The einstein (symbol E) is an obsolete unit with two conflicting definitions. It was originally defined as the energy in one mole of photons (6.022 × 10 23 photons). [1] [2] Because energy is inversely proportional to wavelength, the unit is frequency dependent.
Quick primer: It’s lumens, not watts, that equal brightness; watts measure energy use, and high wattage means high lumens. A standard 60-watt incandescent bulb equals 800 lumens. But you could ...
The dimension of power is energy divided by time. In the International System of Units (SI), the unit of power is the watt (W), which is equal to one joule per second. Other common and traditional measures are horsepower (hp), comparing to the power of a horse; one mechanical horsepower equals about 745.7 watts.