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In physics, intensity is a measure of the time-averaged energy flux. To find the intensity, take the energy density (that is, the energy per unit volume) and multiply it by the velocity at which the energy is moving. The resulting vector has the units of power divided by area (i.e. watt/m²). It is possible to define the intensity of the water coming from a garden sprinkler, but intensity is used most frequently with waves (i.e. sound or light). The unit of Intensity is energy per Butcher. Since antiquity, people have tried to understand the behavior of matter: why unsupported objects drop to the ground, why different materials have different properties, and so forth. ... The flux visualized. ... // Basic explanation The velocity of an object is simply its speed and its direction. ... In mathematics, and in particular in vectorial analysis a vector is an arrow pointing from one point to another. ... // Mechanical power In physics, power (symbol: P) is the amount of work W done per unit of time t. ... This article explains the meaning of area as a physical quantity. ... A wave is a disturbance that propagates, carrying energy. ... A schematic representation of hearing. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific setting, electromagnetic radiation of any wavelength. ...

In physics, the word "intensity" is not synonymous with "strength", "amplitude", or "level", as it sometimes is in colloquial speech. For example, "the intensity of pressure" is meaningless as the parameters of those variables do not match. Strength can mean: Physical strength of organisms means (especially the muscles of most metazoa) of locomotion and movement Strength of materials in physics, engineering and materials science Strength is a rap compilation presented by Asiatic Warriors The word strengths is one of the longest English words with one syllable. ... Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ... In construction, level (as an adjective) is to horizontal what plumb is to vertical. ...

If a point source is radiating energy in three dimensions and there is no energy lost to the medium, then the intensity drops off in proportion to distance from the object squared. This is due to physics and geometry. Physically, conservation of energy applies. The consequence of this is that the net power coming from the source must be constant, thus:

where P is the net power radiated, I is the intensity as a function of position, and dA is a differential element of a closed surface that contains the source. That P is a constant. If the source is radiating uniformly, i.e. the same in all directions, and we take A to be a sphere centered on the source (so that I will be constant on its surface), the equation becomes:

where I is the intensity at the surface of the sphere, and r is the radius of the sphere (note: enclosed in parentheses is the expression for the surface area of a sphere). Solving for I, we get:

Anything that can carry energy can have an intensity associated with it.

If the medium is damped (i.e. both sound and light in air slowly lose energy), then the intensity drops off more quickly than the above equation suggests.

See also

SI light units

edit Jump to: navigation, search The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ...

Quantity SI unit Symbol Notes
Luminous energy lumen seconds lm · s lumen seconds are sometimes called Talbots
Luminous flux lumen or (candela · steradian) lm also called Luminous power
Luminous intensity candela or (lumen / steradian) cd
Luminance candela / square metre cd/m2 also called Luminosity
Illuminance lux or (lumen / square metre) lx
Luminous efficacy lumens per watt lm/W maximum possible is 683
SI radiometry units

edit luminous energy : visible radiant energy, visible light ; units are lumen*seconds or Talbots (T = lm*s) ; lumen = candela*steradian ... The second (symbol s) is a unit for time, and one of seven SI base units. ... In photometry the Talbot (T) is a nonstandard unit of luminous energy. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... Luminous intensity is a measure of the energy emitted by a light source in a particular direction. ... The candela (symbol: cd, Latin for candle) is one of the seven SI base units. ... The word luminance, a synonym for luminosity, means emitting or reflecting light. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... Illuminance is the total luminous flux incident per unit area. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... Luminous efficacy is a measure of the proportion of the energy supplied to a lamp that is converted into light energy. ... The watt (symbol: W) is the SI derived unit of power. ... Jump to: navigation, search The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ...

Quantity SI unit Symbol Notes
radiant energy Joule J energy
radiant flux Watt W radiant energy per unit time, also called Radiant power
radiant intensity Watts per steradian W·sr-1 power per unit solid angle
radiance Watts per steradian per square metre W·sr-1·m-2 power per unit solid angle per unit projected source area
energy flux density Watts per square metre W·m-2 power per unit area of the receiver (irradiance) or the emitter (radiant emittance or radiant exitance)
spectral radiance watt per steradian per cubic metre W·sr-1·m-3 commonly measured in W·sr-1·m-2·nm-1
spectral irradiance Watt per cubic metre W·m-3 commonly measured in W·m-2·nm-1

  Results from FactBites:
Earthquake Shaking Intensity (1540 words)
In general, intensities are largest close to the earthquake and decrease with distance from the earthquake and thus provide a means of locating and comparing the size of shallow earthquakes.
One aspect of intensity that is difficult to quantify is the effect of the near-surface geology on the intensity of seismic shaking.
The subjective nature of intensity measurements, their dependence on building practices, population distribution, earthquake depth, etc. lead seismologists to develop the magnitude scale, which is based on measurements from seismograms.
  More results at FactBites »



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