Summary 2. Electromagnetic Radiation and Quantum Phenomena

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.