2. Photoelectric Effect
First observed by Heinrich Hertz in 1887, the
phenomenon is also known as the Hertz effect.
Hertz observed and then showed that
electrodes illuminated with ultraviolet light
create electric sparks more easily.
3. Photoelectric Effect
The photoelectric effect refers to the emission,
or ejection, of electrons from the surface of,
generally, a metal in response to incident light.
4. Photelectric Effect
In the photoelectric effect, electrons are emitted
from matter (metals and non-metallic
solids, liquids or gases) as a consequence of
their absorption of energy from electromagnetic
radiation of very short wavelength and
high frequency, such as ultraviolet radiation
5. Photelectric Effect
Electrons emitted in this manner may be referred
to as photoelectrons.
The photoelectric effect requires photons with
energies from a few electronvolts to over
1 MeV in high atomic number elements.
Study of the photoelectric effect led to important
steps in understanding the quantum nature of
light and electrons and influenced the formation
of the concept of wave–particle duality.
6. Einstein’s Equations for the
Photoelectric Effect
Einstein's interpretation of
the photoelectric effect
results in equations which
are valid for visible and
ultraviolet light: energy of
photon = energy needed to
remove an electron +
kinetic energy of the
emitted electron
hν = W + E
Where
h is Planck's constant
ν is the frequency of
the incident photon
W is the work
function, which is the
minimum energy required to
remove an electron from the
surface of a given metal: hν0
E is the maximum
kinetic energy of ejected
electrons: 1/2 mv2
ν0 is the threshold frequency
for the photoelectric effect
m is the rest mass of
the ejected electron
v is the speed of the
ejected electron
7. Einstein’s Equations for the
Photoelectric Effect
No electron will be emitted if the incident photon's
energy is less than the work function.
8. In Einstein’s model, a photon is localized that
it gives all its energy hf to a single electron in
the metal. According to Einstein, the
maximum kinetic energy for these liberated
photoelectrons is
Kmax = hf -
ø
The freuency is related to the work function
through the relationship fc = ø/h. The cutoff
frequency corresponds to a cutoff wavelength of
9. Work Functions of Selected
Metals
Metal Ø (eV)
Na 2.46
Al 4.08
Cu 4.70
Zn 4.31
Ag 4.73
Pt 6.35
Pb 4.14
Fe 4.50
