| what is photoemission | a process during which electrons are ejected from a metal surface when exposed to electromagnetic radiation (eg ultraviolet) |
| under what conditions will electrons be liberated from a plate | if the plate is negatively charged
if the source is of a high enough frequency |
| what does intensity of a source affect | the time taken for a negatively charged plate to discharge (as electrons are liberated) |
| does the total amount of energy from the source determine whether the plate discharges or not | no |
| what are beams of light and ultraviolet made of | individual units called photons |
| what must each photon have before an electron can be removed from a negatively charged plate | enough energy to remove the electron |
| what evidence is there that electrons are liberated and not photons | photo emission only occurs from negatively charged surfaces.
The negative charge decreases when this happens, which indicates that negatively charged electrons are leaving the surface |
| what does the energy of a photon depend on | its frequency |
| what does whether photoemission takes place or not depend on | the energy of the photon
the type of metal being tested |
| what is the equation relating energy of a photon to its frequency | E=hf
E is the energy of the photon
h is plancks constant
f is the frequency of the radiation |
| what is plancks constant | 6.63x10^-34 |
| what is threshold frequency (fo) | the minimum frequency required to cause photoemission |
| what is the work function (W) | the minimum energy required to remove an electron from a metal |
| what is the equation relating work function and threshold frequency | W=hfo
where W is work function
h is plancks constant
fo is threshold frequency |
| do different metals have the same or different work functions | different
this means it is easier to remove electrons from some metals than others, therefore the minimum frequency of a photon needed to remove an electron from one mtal can be lower than for another metal |
| what is the relationship between work function and threshold frequency | the lower the work function the lower the threshold frequency |
| when an electron is ejected from a metal surface what kind of energy does it have | kinetic energy |
| what does the amount of kinetic energy an electron being ejected form a metal surface depend on | the difference between the energy of the photon and the work function of the metal |
| give an equation that relates kinetic energy, work function of metal and energy of photon | Ek = E - W
where Ek is kinetic energy of the electron
E is the energy of the photon
W is the work function of the metal
OR
Ek=hf-hfo
Ek=h(f-fo) |
