Electromagnetic Radiation and Quantum Phenomena Flashcards
What is the Photoelectric Effect?
If you shine radiation of a high frequency onto the surface of a metal, it will instantly emit electrons (For most metals, the necessary frequency falls in the ultraviolet range).
The free electrons near the surface of the metal absorb energy from the radiation, making them vibrate.
If an electron absorbs enough energy, the bonds holding it together will break and the electron is released.
What is the first conclusion from the Photoelectric Effect?
For a metal, no photoelectrons are emitted if the radiation has a frequency below a certain value - called the threshold frequency.
What is the second conclusion from the Photoelectric Effect?
The Photoelectrons are emitted with a variety of Kinetic energies ranging from zero to some maximum value, the maximum kinetic energy increases with the frequency of the radiation.
What is the third conclusion from the Photoelectric Effect?
The intensity of radiatopn is the amount of energy per second, hitting an area of the metal. The maximum kinetic energy of the photoelectrons is unaffected by varying the intensity of the radiation/
What is the fourth conclusion from the Photoelectric Effect?
The number of photoelectrons emitted per second is proportional to the intensity of the radiation.
What is Wave Theory?
For a particular frequency of EM waves, the energy carried should be proportional to the intensity of the beam and spread evenly over the wave front.
What is a wave front?
A surface over which the phase of the wave is constant.
How does the Wave Theory link to electrons leaving a metal?
With the wave spread evenly, that means that all of the free electrons on the surface will gain similar energies, per wave front, until it reaches enough to leave the metal. Less energy from the wave would mean it takes longer to leave the metal.
How does intensity link to electrons leaving a metal?
Waves with a higher intensity, will contain more energy (photon energy) to transfer over to the electron.
What is the Work Function?
The Energy required to break the bonds holding the electron in a metal.
What is Excitation?
When an electron jumps up to a higher energy level.
How can electrons de-excite?
By emitting a photon.
How do electrons become excited?
By absorbing a photon.
What is Ionisation?
When the electron has been removed from the atom.
What is the Ionisation energy?
the amount of energy needed to remove an electron from the ground state atom.
Apart from absorbing a photon, how else can electrons gain energy and become excited?
By colliding with other particles.
How do fluorescent tubes use Photon Emission?
A high voltage is put through mercury vapour, which accelerates the free electrons that ionise some mercury atoms. The electrons and atoms collide and the atomic mercury electrons are excited to a higher energy level
How do fluorescent tubes use Photon Emission?
A high voltage is put through mercury vapour, which accelerates the free electrons that ionise some mercury atoms. The electrons and atoms collide and the atomic mercury electrons are excited to a higher energy level. They then de-excite, emitting high-energy photons in the UV range, which is then absorbed by a phosphor coating, exciting its own electrons and then uses the lower energy photons of visible light when the phosphor coating de excites.
