“Spectrum of Black Body Radiation” MHT-CET Class 12 Physics Crash Course | Chapter Kinetic theory of Gases and Radiation
In this session G.S. Khairnar discussed the theory and MCQ’s of “Spectrum of Black Body Radiation”. The session will be useful for all the aspirants of MHT-CET 2022. The session will be in Marathi and English.
Spectrum of Black Body Radiation:-
Hello students we know in previous article we had learnt about the concept of black body. The body which absorbs all the heat radiations incident on its surface is called as perfectly black body.
In practice the perfectly black body cannot be realized. But the lamp black or the platinum black can be considered as a perfectly black body as they absorb more than 98 % of the incident radiant energy.
Spectrum of a black body radiation in terms of wavelength
In 1899, Lummer and Pringsheim performed experiments to study the distribution of energy with the wavelength in spectrum of black body radiations. The intensity of black body radiations corresponding to wavelength ranging from zero to infinity is measured and plotted at various temperatures of black body. The intensity verses wavelength graph is called spectrum.
Different curves are plotted for different values of temperatures of black body shown in fig.
Following are the conclusions that can be drawn from the graph,
At given temperature of black body
- The energy emitted is not distributed uniformly among all wavelengths.
- The energy emitted is maximum for wavelength λmax and it falls on either side of it. The wavelength is called wavelength of maximum emission.
With rise in temperature of black body
- The energy emitted increases rapidly for any wavelength.
- The wavelength for which energy emitted is maximum and shifted towards shorted wavelength side.
Important law related to spectrum of black body radiation…..!
- Wien’s displacement law
The wavelength (λm) corresponding to maximum energy emitted by a black body is inversely proportional to its absolute temperature.
This law is used to find the temperature of the sun and stars.
Spectrum of Black Body Radiation:-
Let’s solve the following MCQs ……..!
Q.1) According to spectrum of black body radiation, the wavelength for which energy is maximum when temperature increases is………
a) remains same with increase in temperature
b) increases with increase in temperature
c) decreases with increase in temperature
d) initially increases and then decreases
Answer
c) decreases with increase in temperature
Q.2) The wavelength for which the energy is maximum is ………
a) directly proportional to absolute temperature of black body
b) inversely proportional to absolute temperature of black body
c) directly proportional to square of absolute temperature of black body
d) inversly proportional to square of absolute temperature of black body
Answer
a) directly proportional to absolute temperature of black body
Q.3) The value of Wien’s constant is given as………
a) 9х10-3cm.K
b) 9х10-3 m/K
c) 9х10-3K/m
d) 9х10-3 m.K
Answer
d) 9х10-3 m.K
Q.4) The ratio of absolute temperatures of black body is 2:3, the ratio of maximum emission wavelength is………
a) 2 : 3
b) 3 : 2
c) 4 : 9
d) 9 : 4
Answer
b) 3 : 2
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