Section 2:
Electromagnetic Radiation and Quantum Phenomena
The Photoelectric effect
If radiation of a high enough frequency is directed to the surface of the metal, it will emit
electrons.
Metals have free electrons that are able to move throughout
the metals structure; the electrons on or near the metals
surface will absorb energy from the radiation, making them
vibrate.
If the electrons absorb enough energy beyond the threshold
frequency – they will be emitted from the metals structure
Conclusions for this experiment:
For a given metal, no photoelectrons are emitted if the radiation has a frequency below a
certain value – threshold frequency
The photoelectrons emitted with a variety of kinetic energies ranging from 0 to a maximum
value. The maximum kinetic energy increases with the frequency of the radiation
The intensity of radiation is the amount of energy per second hitting an area of metal. The
maximum kinetic energy is not affected by the intensity
The number of photoelectrons emitted per second is proportional to the intensity of the
radiation
The Photoelectric effect and wave theory
Threshold frequency :
Wave theory states that, for a particular frequency of EM wave, the energy should be proportional to
the intensity of the beam. The energy should also be spread evenly over the surface of the metal.
Therefore following wave theory, even lower frequency would transfer a bit of energy to each
free electron.
Gradually, each free electron would gain enough energy to be omitted.
And therefore, lower frequency (energy) waves would take longer to cause photo electrons to
be released, but in the end the electrons should be released.
Electromagnetic Radiation and Quantum Phenomena
The Photoelectric effect
If radiation of a high enough frequency is directed to the surface of the metal, it will emit
electrons.
Metals have free electrons that are able to move throughout
the metals structure; the electrons on or near the metals
surface will absorb energy from the radiation, making them
vibrate.
If the electrons absorb enough energy beyond the threshold
frequency – they will be emitted from the metals structure
Conclusions for this experiment:
For a given metal, no photoelectrons are emitted if the radiation has a frequency below a
certain value – threshold frequency
The photoelectrons emitted with a variety of kinetic energies ranging from 0 to a maximum
value. The maximum kinetic energy increases with the frequency of the radiation
The intensity of radiation is the amount of energy per second hitting an area of metal. The
maximum kinetic energy is not affected by the intensity
The number of photoelectrons emitted per second is proportional to the intensity of the
radiation
The Photoelectric effect and wave theory
Threshold frequency :
Wave theory states that, for a particular frequency of EM wave, the energy should be proportional to
the intensity of the beam. The energy should also be spread evenly over the surface of the metal.
Therefore following wave theory, even lower frequency would transfer a bit of energy to each
free electron.
Gradually, each free electron would gain enough energy to be omitted.
And therefore, lower frequency (energy) waves would take longer to cause photo electrons to
be released, but in the end the electrons should be released.
