Introduction to Quantum Physics
The characteristics of blackbody radiation cannot be explained using classical
concepts.
Planck first introduced the quantum concept when he assumed that the atomic
oscillators responsible for this radiation existed only in discrete states.
The
photoelectric effect
is a process whereby electrons are ejected from a metallic
surface when light incident on that surface.
Einstein provided a successful explanation of this
effect by extending Planck’s quantum hypothesis to the electromagnetic field.
In this model,
light is viewed as a stream of particles called photons, each with energy E = hf, where f is the
frequency and h is Planck’s constant.
The kinetic energy of the ejected photoelectron is
given by
φ

=
hf
K
max
where
φ
is the work function of the metal.
Xrays from an incident beam are scattered at various angles by electrons in a target
such as carbon.
In such a scattering event, a shift in wavelength is observed for the scattered
xrays, and the phenomenon is known as the
Compton effect
.
Classical physics does not
explain this effect.
If the xray is treated as a photon, conservation of energy and momentum
applied to the photonelectron collisions yields the following expression for the Compton
shift:
)
cos
1
(
θ
λ

=
∆
mc
h
where m is the mass of the electron, c is the speed of light, and
θ
is the scattering angle.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Light has a dual nature in that it has both wave and particle characteristics.
Every
object of mass m and momentum p has wavelike properties
.
The
de Broglie wavelength
of
an object with momentum p
is given by
p
h
=
λ
By applying this wave theory of matter to electrons in atoms, de Broglie was able to explain
the appearance of quantization in the Bohr model of hydrogen as a standing wave
phenomenon.
The
uncertainty principle
states that if a measurement of position is made with
precision
∆
x and a simultaneous measurement of momentum is made with precision
∆
p
x
,
then the product of the two uncertainties can never be smaller than a number of the order of
h /2.
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '10
 MichelA.VanHove
 Angular Momentum, Quantum Physics, Planck

Click to edit the document details