Reduction of Planck�s law to Wein�s law and Rayleigh Jeans law:
i) For shorter wavelengths, υ = c/λ is large.
When υ is large, ehυ/kT is very large.
.
.
. e
hυ/kT >> 1
.
.
. (ehυ/kT
-1) ≈ ehυ/kT = ehc/λkT
Substituting in eqn 1:
Uλ dλ =
d
hc
5 hc/ kT e
8 1
=
C e d
T
C
......

Reduction of Plancks law to Weins law and Rayleigh Jeans law:
i) For shorter wavelengths, υ = c/λ is large.
When υ is large, ehυ/kT is very large.
.
.
. e
hυ/kT >> 1
.
.
. (ehυ/kT
-1) ≈ ehυ/kT = ehc/λkT
Substituting in eqn 1:
Uλ dλ =
d
hc
......

Module - 1
1.
a Mention the assumptions of Plancks law. Arrive at the relation
for Weins law from Plancks law. 6 M
b State Heisenbergs uncertainty principle. Show that electrons
cannot exist inside the nucleus.
6M
c Calculate the de-Broglie wavelength associated with neutron of
mass 1.674 X 10-27 kg with one tenth part of the velocity of light.
4M
Ans (a).
i) P......

Module - 1
1.
a State Plancks radiation law. Show how Plancks law could be
reduced to Wiens law and Rayleigh Jeanss law. 7 M
b State Heisenbergs uncertainty principle and Show that electrons
cannot exist inside the nucleus by this principle.
5M
c Find de-Broglie wavelength of a particle of mass 0.58 MeV/c2 has
a kinetic energy 90 eV, where c is the velocity of light.
......

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