Emissivity

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Emissivityis the energy of light emitted by an object, the energy of light emitted by the same temperature (1) , Respectively. It is a value (0) of 0 or more and 1 or less, depending on the substance and the wavelength of light.

Emissivity ε and α are equal:

ε = α

Also, when light of a certain wavelength strikes an object, the sum of ρ, τ and absorptance α becomes 1:

ρ + τ + α = 1

If the object is thick enough, the transmittance τ will be zero. Then

ρ + α = 1

. Using the above Kirchhoff's law for this equation

ρ = 1 - ε

. That is, the reflectance is small if the emissivity ε is large, and the reflectance is large if the emissivity ε is small. From this, it is understood that in order to reflect light as possible, it is necessary to cover the surface of the object with a material with a low emissivity.

For example, the surface of a firefighter wears is coated with metal because the emissivity of the metal is low (high reflectance) at a wide range of wavelengths. By reflecting thermal radiation emitted from a high temperature object, it protects the body of the firefighter from high temperatures.

Example value

For each substance, the emissivity ε has the following value.

• Aluminum 0.02-0.1
• Iron (oxidized surface) 0.5 - 0.9
• Rubber 0.95
• Ceramic 0.95

Acquired from ""

Post Date : 2018-02-26 05:00

This article is taken from the Japanese Wikipedia Emissivity

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