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Current Category » Agricultural Meteorology

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Laws Of Radiation

The radiation reaching to the earth surface from the sun, atmosphere and from earth to atmosphere, space follows certain physical laws known as radiation laws. They are

  1. Plank’s Law:

The Electro magnetic radiation consists of a stream or a flow of particles or quanta.  Each quantum having energy content
E=hv. Where, h=Plank’s constant (6.625x1027 ergs sec-1)
V=frequency of Electro-magnetic length.
Greater the frequency (i.e. shorter the wave length) greater is the energy content of the quantum.

  1. Stefan Boltzman’s Law:

The intensity of radiation emitted by a radiating body is proportional to the fourth power of its absolve temperature.
Where E=Emissive of the body
S=Stepen’s constant (5. 67x10-8W m-2.K-4)
T=surface temp of the body in absolute 0K

3. Weins displacement Law:
The wave length of maximum intensity of emission is inversely proportional to the absolute temp, o f that body.
µ Max (um) =2897 T
For example, the temp. of earth surface is 2870K then its peak emission will be close to 10 µ similarly for the sun having temp, of 6000 0K it will peak at 0.5π

  1. Kirchoffs Law:

Kirchoffs Law state that the absorptivity of a material for a radiation of a specific wave length is equal to its emissivity for the same wave length at same temperature.

Current Category » Agricultural Meteorology