Quantum Flashcards
what is a photon
a quant of energy
what is planks constant
6.63 x 10^-34
what are the equations linking planks constant to energy
E = hf
E = hc/λ
describe the photoelectric effect
When electromagnetic radiation above a threshold frequency (a high enough frequency) is incident on a metal, electrons are emitted from the surface of the metal. One electron absorbs the energy from one photon and the emitted electrons are called photoelectrons.
define threshold frequency
The minimum frequency needed of electromagnetic radiation that will cause the emission of an electron from the surface of a particular metal. Measured in Hertz.
define work function
The minimum energy needed to remove a single electron from the surface of a given metal (the value is dependent on the metal).
how does changing intensity affect electron emmision
a higher intensity leads to a higher number of photons emitted per second, so a higher rate of electron emission, but not an increase in the speed of the electrons because it doesnt change the actual energy supplied to each electron.
whats the relationship between a photon and an electron
an electron can only absorb one photon
this is the reason to why intensity doesn’t affect an electrons energy
Why does the photoelectric effect formula refer to maximum ke rather than simply ke
?
The work function is the minimum energy required to emit an electron from the surface of a metal
This means that it may take more energy than this for the electron to be emitted - i.e. the final calculated kinetic energy is a maximum, and may be lower.
Why was graphite a suitable material for de Broglie’s electron diffraction experiment?
The spacing between atoms in graphite is approximately the same as the de Broglie wavelength of the electrons passing through
what does intensity of a source represent in terms of wave particle duality
The intensity of a wave at a point in space represents the probability of a particle being there.
This is an important part of wave-particle duality, and goes some way to explaining how an electron can be both a wave and a particle - we can only ever know the likelihood, or the probability, of the electron being one or the other as it moves between particle and wave behaviour.
what is wave particle duality
Electromagnetic radiation can display both wave and particle properties; matter can display both wave and particle properties.
give the de broglie equation
de broglie wavelength is equal to planks constant divided by momentum
which experiment proves that waves can behave like particles
the photoelectric effect with gold foil experiment
which experiment proves that particles can behave like waves
Demonstrating wave-particle duality requires two results: showing that waves can behave like particles and showing that particles can behave like waves.
Electron diffraction showed that particles can behave like waves. The diffraction pattern created by electron diffraction gives evidence for the wave nature of electrons (or particles more generally)
give an an example of light acting as a wave
diffraction
interference
polarisation
refraction
give an an example of light acting as a particle
the photo electric effect
give an example of electrons acting as particles
deflection of electrons by a magnetic field, and collisions with other particles
give an example of electrons acting as a wave
electron diffraction
give the de broglie equation
wavelength = planks constant ÷ momentum
what is the optimal slit width for electron diffraction and what does this mean
for the best diffraction you should have a slit width equal to the de droglie wavelength
what is stopping potential
minimum electric potential that needs to be applied to a charged particle to completely halt its motion
