Quantum phenomena Flashcards
(28 cards)
what happens when you shine light on the surface of a metal
delocalised electrons on the surface of the metal absorb energy , the bonds holding it to the metal break and the electron is released this is called the photo electric effect and the electrons emitted are called photo electrons
what is the threshold frequency
for a given metal , no photoelectrons are emitted if the radiation has a frequency bellow a certain value this is called the threshold frequency
what is a conclusion that can be made about the photelectric effect and kinetic energy
the photo electrons emitted have a variety of kinetic energy’s from 0 to the maximum. this value of the maximum kinetic energy increases with the frequency of the radiation and if unaffected by the intensity of the radiation.
what is the third conclusion on the photo electric effect that can be made to do with intensity
the number of photoelectrons emitted per second is proportional to the intensity of the radiation
how does wave theory not support the kinetic energy depending on the frequency
according to wave theory for a particular frequency of light the energy carried away is proportional to the the intensity of the beam so the higher the intensity if the wave the more energy it should transfer to each electron the kinetic energy should increase with intensity however it actually depends on the frequency not the intensity and there is no explanation for this
how does wave theory not support the threshold frequency
according to wave theory each delocalised electron on the surface on the metal would gain a bit of energy from each incoming wave and gradually each electron would gain enough energy to leave the metal however this does not happen infract no electrons will leave if the wave is not above the threshold frequency there is no explanation for this
what is Einstein’s photon model of light
Einstein suggested that electron magnetic waves exist in discrete packets called photons and these photons have a particle like reaction with the electrons transferring all its energy to one electron.
according to the photon model what happens when EM radiation is shone on a metal
when the light hits the metals surface the metal is bombarded with photons. if one of these photons collide with a delocalised electrons the electron will gain energy equal to its frequency times planks constant.
what is the work function
before an electron can leave the metal it needs enough energy to break the bonds holding it there this is called the work function and its value depends on the material
how does the photon model explain the threshold frequency
if the energy gained by an electron from a photon is greater than the work function the electron is emitted.
if it isn’t the metal will heat up but no electrons will be emitted
how does the photon model explain the maximum kinetic energy
the energy transferred to the electrons is equal to the planks constant times it frequency
the kinetic energy of the electron is that value minus the energy taken to leave the metal.(electrons deeper down in the metal lose more then the surface ones explaining the range in KE)
the minimum amount of energy an electron can lose is the work function this gives the maximum KE .
using the photon model why does increasing the intensity of light not increase the maximum kinetic energy
a electron can only absorb one photon so higher intensity means more electrons released but not an increase in the kinetic energy of those electrons
what is the stopping potential
the maximum kinetic energy can be measured using the stopping potential as the electrons emitted are having to do work again the potential different applied.
the stopping potential is the p.d. needed to stop the fastest moving electrons and the work done by the p.d. in stopping the fasts electron is equal to the energy they were carrying
how can electrons move down energy levels
emitting a photon although because these energy levels are certain values the energy of each photon emitted can only take a certain value allowed.
what is a electronvolt
the kinetic energy carried by an electron after it has been accelerated from rest through a potential difference of 1 volt
when an electrons emits a photon to move down energy levels what’s the value of the photon
the energy carried by each photon is equal to the differences in energies between the two levels.
how can electrons move up energy levels
if they absorb a photon with the exact energy difference between the two energy levels.
this movement of an electron up an energy level is called excitation.
how can an electron leave an atom
when an electron fully leaves the atom we say it is ionised. the energy of each energy level is the energy needed to remove an electron from that level.
what is the ionisation energy
the amount of energy needed to completely remove an electron from the atom from the ground state
how do fluorescent tubes produce light
florescent tube contain mercury vapour across which a high voltage is applied. this voltage accelerates fats moving electrons that ionise the mercury atoms producing more free electrons.
where the free electrons collide with the mercury atom they excite the electrons.
when the excited electrons return to their ground state they emit photons in the UV range.
a phosphor coating absorbs the photons exciting its electrons and then when they return to the ground state they emit many low energy photons in the form of visible light.
what happens when you shine a florescent tube through a prism or diffraction grating
a line spectrum of bright lines against a black background.
each line is a wavelength of light emitted
since only certain photon energies are allowed you only see the corresponding wavelengths to these energies.
how can you seen the spectra of light and how does this relate to hot things
shine white light through prism will give a spectra of colours with no gaps
hot things emit a continuous spectra of infrared and visible light as the electrons are not confided to energy levels in the object producing a continuous spectrum
what happens when white light passes through a cool gas
at low temperatures most electrons in the gas atoms will be in there ground state. the electrons can only absorb photon with the exact amount of energy to move up energy levels. so these photons with the corresponding wavelengths are absorbed leaving gaps on the spectrum this is the opposite of an excited gas
how is light shone to act like a wave
light produces interference and diffraction pattens which can only be explained by waves interfering constructively and destructively
