Wien’s Distribution Law


Q.Define Wien’s  distribution law.

A. Wien’s approximation also called  Wien’s distribution law is a law of physics used to describe the spectrum of thermal radiation frequently called the blackbody function.

Q.Define Wien’s displacement law.

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

Q.What is a black body?

A. A black body is one that absorbs all incident electromagnetic radiations and once it reaches thermal equilibrium emits electromagnetic radiations called black body radiations.

Q.What kind of solar cell is used?

A.Photo-voltaic cell– Cellinium type.

Q.Define photo-voltaic effect.

A.The “photovoltaic effect” is the basic physical process through which a solar cell converts sunlight into electricity

Q.Why do we use different filters?

A.So as to allow light of only certain frequency to pass.

Q.What is the value of Boltzman constant?

A.      kB=   1.387 x 10^-23 Joules/Kelvin

Q.What is Planck’s law?

A.Planck’s law describes the electromagnetic radiation emitted by a black body in thermal equilibrium at a definite temperature.

Q.What is Rayleigh-Jeans law?

A. Rayleigh–Jeans law attempts to describe the spectral radiance of electromagnetic radiation at all wavelengths from a black body at a given temperature through classical arguments.

Q.What was so special that Planck’s law overrode wein’s and Rayleigh’s?

A. Lord Rayleigh‘s hypothesis may be used to accurately describe the long wavelength spectrum of thermal radiation but fails to describe the short wavelength spectrum of thermal emission,similarly Wein’s  law is true for short wavelength but fails for long wavelengths.But Planck’s law is true for the entire spectrum.

Q.Define Draper current.

A.It is the minimum current required to just ignite the filament of the bulb.

Q.Why do we assume that the bulb is a black body?

A.This is so because the condition to create a black body artificially is to enclose the light source in a container and provide a  single thin & narrow outlet of light.

Q.What is the standard value of planck’s constant?

A.                h = 6.626 × 10-34 Joule-sec

Q.Can we use photoelectric effect in place of this method to calculate Planck’s constant?

A.Yes,we can use it because in both light energy is converted to electrical energy.

According to classical physics as the temperature rises so does the energy so hypothetically at some temperature the energy possessed by the object would become infinite but it is not so.Later on Planck’s said that each wave has an intrinsic energy independent of temperature.


Please do study this graph–>

DO read about black body and planck’s law.

Weins displacement law



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