Chapter 27
Wien’s Displacement Law:
λ
max
(T) = 0.2898 x 10^2
(m x K)
where
λ
max
is the wavelength at which the curve peaks and T is
the absolute temperature of the object emitting the radiation
Classical theory says that predicts that intensity of blackbody
radiation should be infinite but experimental data shows that is
should approach zero
ultraviolet catastrophe
Resonators have discrete energies E
n
, given by
E
n
= nhf
where n is a positive integer called a quantum
number, f is the frequency of vibration of the resonator, and h
is Planck’s constant,
h = 6.626 x 10
34
(J x s)
When
∆
V is equal to or more negative than 
∆
V
s
, the stopping
potential, no electrons reach C and the current is zero.
The
stopping potential is independent of the radiation intensity.
The maximum kinetic energy of the photoeletrons is related to
the stopping potential through the relationship,
KE
max
= e

∆
V
s
The maximum kinetic energy for liberated photoelectrons is
KE
max
= hf 
φ
Where
φ
is called the work function of the metal, the
minimum energy with which an electron is bound in the metal,
can be found in a table
Diffraction of Xrays by crystals: the condition for
constructive interference is
2dsin
Θ
= m
λ
, where m = 1, 2, 3….
The change in wavelength between a scattered xray and an
incident ray is called the Compton shift:
∆λ
=
λ

λ
0
= h/m
e
c x (1cos
θ
)
where m
e
is the mass of the electron and
Θ
is the angle
between the directions of scattered and incident photons, The
quantity h/m
e
c is called the Compton wavelength and has a
value of 0.00243 nm.
The Compton shift depends on the
scattering angle and not the wavelength.
Energy of a photon:
E = hf = hc/
λ
Momentum of a photon:
p = E/c = hc/c
λ
= h/
λ
So, the de
Broglie wavelength of a particle is
λ
= h/p = h / mv
Further, frequency of waves is
f = E/h
The uncertainty principle: If a measurement of the position of
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 Fall '07
 SPITZER
 Atom, Energy, Photon, Light, Planck

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