Quantum Particles Flashcards
What is the Photoelectric equation?
max kinetic energy = (planks constant x frequency) + work function
Ek(j) = hf(hz) - phi(j)
What is meant by the work function?
It is the minimum energy required in order for the electron to be liberated from the metal
Size of it is dependant on the metal
What effects the amount of kinetic energy an electron has when it leaves the metal?
How far away from the surface the electron is, the further from the surface the less the kinetic energy it leaves with
Energy of the photon hitting the metal, the higher the energy the more energy the electron will have
Equation for a threshold frequency of a metal?
work function = planks constant x threshold frequency
phi = h x f0
What are the key points of the photo electric effect?
One to One interaction between a photon and an electron
The frequency of the photon needs to be larger than threshold frequency to overcome the work function
100% of the photon must be absorbed
Emission is instant and proportional to the intensity of light
What is ‘stopping potential’?
It’s the reverse potential difference needed to stop an electron at max kinetic energy
What are the rules for exciting and de exciting electrons?
Electrons can only exist at set discreet energy levels (cant be halfway between)
When an electron moves up an energy level it gains from photons or heat or other electrons etc
When an electron moves back down energy levels, the energy it has gained is emitted in the form of photons
Equation for stopping potential?
electron charge x stopping potential = max kinetic energy
e(j) x Vs (v) = Ek (j)
1 ev is equal to?
1eV = 1.6 x 10 ^-19 (j)
How can an electron move up an energy level?
It can move up an energy level if it absorbs a photon with the exact energy difference it needs to get to any of the higher energy levels
How can you measure the energy and thus frequency of a photon emitted from an electron moving down energy levels?
Measure the difference between the energy levels it has moved between:
E1 - E2 = Delta E
Then use E=hf to calculate the frequency of the photon
What is ionisation energy? How is it calculated?
its the energy required to move an electron from the ground state to n = infinity (remove the electron from the atom)
Find the energy difference between the ground state and the n = 0/infinity
Explain how the excitation and de excitation phenomena and the photoelectric effect applies to a fluorescent light
When light is turned on one end of flourescent tube becomes live
The voltage accelerates the electrons
Electrons collide with the electrons in the Mercury and create more free moving electrons
The free electrons from the Mercury atoms and voltage, collide with other Mercury electrons and excite them
When the electrons de excite, they release photons in the UV spectrum
The photons are then absorbed by the phosphor coating on the tube and excite its electrons to higher energy levels
The electrons then de excite bit by bit emitting many lower energy photons in the visible light form
Define an electron volt (eV)
the kinetic energy carried by an electron after it has been accelerated through a potential difference of 1 volt
