3.2.2 Electromagnetic Radiation And Quntum Phenomena Flashcards
What effect does :
.Increasing intensity of incident EM radiation
,Increasing the frequency of incident radiation
Have on the emission of photoelectrons?
.increases the number of photoelectrons emitted per second
.increases the max KE of emitted photoelectrons
Explain why the photoelectric effect could not be explained by the wave model of light
Each electron would only gain a tiny amount of energy from each wave
This would build up until the electron has enough energy to be freed
Therefore the model dosent explain the minimum energy requirement of photons and would result in a delay between the incident photon and electron emission.
Define the work function of a metal
The minimum energy required to remove an electron from the surface of a metal.
Describe the graph of the relationship between frequency of em radiation and max KE
A straight line that intercepts the y axis at -work function and the x axis at minimum frequency. Its gradient is equal to Plancks constant.
Define stopping potential giving its equation
The PD required to stop the emission of photoelectrons.
Vs = Ekmax/e
Why are the energy levels in an energy level diagram negative?
Energy must be supplied for an electron to move up a level and emitted for an electron to move down a level. Furthermore energy must be 0 for a free electron and therefore the levels below it have a negative energy level
What can cause excitation?
When an electron absorbs the entirety of a single photon with exactly enough energy to move up a level(s)
When a free electron collides with the orbital electron transferring some of its KE equal to the difference in energy levels
What will de-excitation result in?
The electron will move back to its original energy level and there will be a photon with exactly equal energy to the energy change emitted.
What are the two ways an electron can de-excite?
It can either jump straight back down to its origional energy level
Or it can cascade down emitting multiple photons of smaller energies
Define ionisation energy
The amount of energy required to completely remove an electron from the atom starting at the ground state
How are line emission/absorption spectrum produced
Passing light through excited/cool gas will result in the emission/removal of certain wavelengths of light the light leftover after this can then be split by a prism as different wavelengths are diffracted differently and so there will be stand out lines on a continuous spectrum
Describe diffraction and the factors affecting it
Diffraction is the spreading out of waves as they pass through a gap the size of which is the same order of magnitude as the wavelength of the wave.
Smaller gap size will result in a greater diffraction effect
A larger wavelength will also result in a greater diffraction effect
Describe the process of electron diffraction
Electrons are accelerated in an electron gun and fired through a thin sheet of graphite to cause diffraction as the electrons pass through the gaps between the carbon atoms.
This causes a circular pattern to appear on a fluorescent screen proving the electrons have been diffracted.
Why can’t diffraction be observed with larger particles?
A larger particle requires an incredibly small gap due to de broglies equation which the particle wouldn’t be able to fit through and is also to small to interact with
