Modern
Physics
Photoelectric Effect
Planck's
Constant
(2)
E = hf
Where
h is 
or 
.
Photoelectric
effect: radiant energy (in the form of X-rays, ultraviolet, or
light) impinging on various metals ejects electrons from their
surfaces.
Planck's
Equation 2
(3) 
Einstein's
Photoelectric Equation
(4) 
Where 
is
the work function.
Photoelectric
Effect Activity
Example
3
Suppose
the maximum speed of a 1.2 kg mass attached to a spring with
a force constant of 35 N/m is 0.95 m/s. (a) Find the frequency
of oscillation and total energy of this mass-spring system. (b)
Determine the size of one quantum of energy in this system. (c)
Assuming the energy of this system satisfies 
,
find the quantum number n.
Solution:
(a) 
(b) 
(c) 
Example
4
Calculate
the energy of a photon of yellow light with a frequency of 
.
Give the energy in both joules and electron volts.
Solution:
Example
5
Molecular
oxygen (
)
is a diatomic molecule. The energy required to dissociate 1 mol
of to
form 2 mol of atomic oxygen is 118 kcal. (a) Find the energy
(in joules and electron volts) required to dissociate one molecule.
(b) Assuming the dissociation energy for one molecule is supplied
by a single photon, find the frequency of the photon.
Solution:
(a) 
(b) 
Cutoff
Frequency:
or
the minimum wavelength:
Example
6
The
work function for a gold surface is 4.58 eV. Find the cutoff
frequency for a gold surface.
Solution:
Example
7
A
beam of white light containing frequencies between 
and
is
incident on a sodium surface, which has a work function of 2.28
eV. (a)
What is the range of frequencies in this beam of light for which
electrons are ejected from the sodium surface? (b) Find the maximum
kinetic energy of the photoelectrons that are ejected from this
surface.
Solution:
(a) 
Therefore
the beam will eject electrons for frequencies between 
and .
(b) 
On
to more Photoelectric effect
