Special Distribution of Blackbody Radiation - Wien's Law

Physics

law

Wien's displacement Law

Wien's displacement law states that the black body radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature.

where T is the absolute temperature in kelvin. b is a constant of proportionality called Wien's displacement constant, equal to

diagram

Spectrum of blackbody radiation vs wavelength at different temperatures

Intensity increases with temperature and peak wavelength decreases with temperature

definition

Heat detection devices

Bolometer and Thermopile are two devices to measure radiation.
Bolometer
It is based on the working principle of the Wheatstone bridge. A thin foil of platinum is cut into strips in a grid like pattern. Four such identical grids are taken to form a Wheatstone bridge with a battery and a galvanometer connected. Grids 1 and 4 are allowed to fall radiation upon whereas grids 2 and 3 are protected from radiation. At balance condition the resistances of the grids are related as:
where are the resistances of the grid.
As temperature increases on radiation, and increases but the product remains constant. This brings about a deflection in the galvanometer which is a measure of radiation.
Thermopile
It works on the principle of Seeback effect. A thermopile s composed of a number of thermocouples made from bismuth and antimony in a series connection to increase the sensitivity of the system. The free ends are connected to a galvanometer. The junctions are arranged in such a way that all the hot junctions lie on a plane face and all the cold junctions lie on the opposite plane face.The face of the hot junctions is blackened and exposed to radiation while the other face is shielded.  A metallic cone generally concentrates the radiation on the hot face. The radiation is measured by the deflection in the galvanometer.

REVISE WITH CONCEPTS

What is Radiation?

ExampleDefinitionsFormulaes

Stefan Boltzmann Law

ExampleDefinitionsFormulaes
LEARN WITH VIDEOS

Quick Summary With Stories

Important Questions
View solution
>
View solution
>
View solution
>
View solution
>
View solution
>
View solution
>
View solution
>
26719
expand
View solution
>
View solution
>
View solution
>