Photoeletric Effect Flashcards
What is the photoeletric effect?
When light hits a metal surface, lierating electrons to move out of the surface
What does the intensity of light affect?
The number of electrons liberated
What does the frequency of light affect?
The kinetic energy of the electrons liberated
What is the cutoff voltage?
The cutoff voltage is the minimum negative voltage where the current of circuit is 0. It is also essentially the maximum Ek of emitted electron in electron volts.
What is the work function?
The work function is the minimum energy need for an electron to move out of from surface of metal.
To release an electron, it must gain enough energy to overcome the attraction of the positive nuclei in metal.
What is the threshold frequeny?
The threshold frequency is the minimum frequency required by the electron to move out of metal surface
Why is a greater cutoff voltage required for a light that emits higher frequency photons?
At cutoff voltage all Ek converts to Ep before electron reaches other plate. As Ep = qv, a greater voltage is needed to change Ek of electron to Ep
What is the wave theory for intensity of light?
Intensity of light should determine Ek of liberated eleectrons, eg a brighter light should released electron with greater Ek
What is the wave theory for frequency of light?
frequency of light should have no effect on the number or energy of electrons liberated. eg. all frequencies should release electron with same energy.
What is the wave theory for metals?
type of metal that light shines on should have no effect on number of e liberated at a particular frequency. Eg. all metals should have same threshold frequency
The closer the energy levels…
the less energy
Why must the photon’s energy be greater than the work function?
since one photon absorbs one electron, the photon must have greater energy than work function so that electron has enough energy to overcome the attraction to the positive nuclei and escape the mtetal. Any energy above that to escape the metal will contribute to the electron’s EK>
Why must photons be of exact energy when moving electron up an energy level?
Electrons inside atom of low desntiy gas can only occupy specific energy lelvels. Energy of photon used to life electron to higher energy level, must provide exactly the difference in energy between the levels. If the enrgy of the photon does not match the energy level difference, the electron will not absorve the photon. Thus specific energy of photon is needed to move electron up energy levels because of specific quantised energy levels.
Why do we focus on the minium energy of a photon when releasing electrons from a metal surface?
When energy of photon is large enough, it can release electron from atom overcoming the electron’s coulomb attraction to nucleus. Once freed, any excess energy is converted to Ek of electron. Therefore any value above needed to realase the electro form atom can be absorbed by electron
Describe and explain one piece of experimental evidence which shows that light is not simply a wave, but that it also has a particle nature.
Photoelectric effect: THRESHOLD FREQUENCY - There is no emission of electrons when the surface is illuminated with light below a threshold frequency, however intense the light is. This suggest that the light is interacting with the surface in discrete amounts of energy. If the energy of this photon is too low then no electron emission can occur. Meaning light energy is quantised.
