3.2.2.1 Particles and Radiation: The photoelectric effect Flashcards
What is the photoelectric effect?
When light of a high enough frequency is incident on the surface of a metal, electrons are emitted from the surface of the metal
Explain the photoelectric effect
Metals contain free electrons that are able to move around in the metal. The free electrons on or near the surface of the metal absorb energy from the radiation, making them vibrate. If an electron absorbs enough energy, the bonds holding int to the metal can break and the electron can be released (called the photoelectric effect).
What are photoelectrons?
Electrons that have been emitted from a metal through the photoelectric effect
What is threshold frequency?
For a given metal, no photoelectrons are emitted if the radiation has a frequency below this value
What is the range of kinetic energies of photoelectrons?
A variety - ranging from zero to some maximum value. The value of MAXIMUM kinetic energy increases with the frequency of the radiation.
What is intensity?
The amount of energy per second hitting an area of the metal. (it does not affect the maximum kinetic energy of photoelectrons)
What is the relationship between the number of photoelectrons emitted per second and the intensity of radiation?
The number of photoelectrons emitter per second is proportional to the intensity of radiation.
How does intensity affect kinetic energy of the photoelectrons?
Kinetic energy increases with intensity
What did Einstein suggest about EM waves?
They can only exist in discrete packets (called photons). He saw these as having a one-on-one particle like interaction with an electron in a metal surface. Each photon would transfer all its energy to one specific electron (photon model used to explain the photoelectric effect)
Why to photoelectrons have a maximum kinetic energy?
The maximum amount of energy that can be transferred to an electron is the energy of one photon. The maximum amount of kinetic energy an electron can have is the energy of one photon minus the work function energy (as there is a minimum amount of energy needed to free the electron from the metal)
What is stopping potential?
Photoelectrons emitted by the photoelectric effect can be made to lose their energy by doing work against an applied potential difference. The stopping potential is the p.d. needed to stop the fastest moving electrons travelling with the maximum kinetic energy. The work done by the potential difference in stopping the fastest electrons is equal to the energy they were carrying.
How can the maximum kinetic energy be measured?
Using the idea of stopping potential
What is the formula for stopping potential?
e(charge of electron)* (stopping potential (V) = (maximum kinetic energy (J))
What is the formula for the energy of a photon?
E = hf = (hc)/lambda
What is the work function?
The minimum energy needed for an electron to break its bonds and leave the metal
