From the blackbody radiation spectrum, we learned that the wavelength for which intensity of radiation is maximum decreases as temperature T is increased.
Thus,
λmaxα 1/T
λmax = b*1/T
And here b is the constant which is called as Wien’s constant whose value is 2.898*10-3mK.
Statement:
According to Wien’s Displacement law, the wavelength is inversely proportional to the absolute temperature of the blackbody for which emissive power of the blackbody is maximum.
Explanation:
This law is named as displacement law because all we know that as temperature is increased the maximum intensity peak is shifted towards the shorter and shorter wavelength.
Emissive power:
The emissive power of the body is defined as it is the radiant energy emitted by the body per unit time per unit surface area of the body at a given temperature.
Hence, emissive power can be given as
E = Q/At
The SI unit of emissive power is J/m2s or W/m2.
And the dimensions of emissive power will be [M1 L0 T-3].
The emissive power of the body depends on mainly following factors:
- temperature of the given body
- nature of the given body
- nature of the surroundings
- surface area of the body
The emissive power of the perfectly blackbody is greater than any other bodies always.
For example:
Lampblack is having emissive power as 98%.
Applications:
The Wien’s Displacement law is used to find the very high temperature of bodies like distant stars, sun, moon, celestial bodies etc.