2.2 Electromagnetic radiation and quantum phonomena Flashcards
Are electromagnetic waves transverse or longitudinal?
Transverse
What phenomenon can be used to show that light acts like a particles?
The photoelectric effect
Describe the photoelectric effect.
When light above a certain frequency is shone at a metal, electrons are released. These released electrons are called “photoelectrons”
What is the threshold frequency ?
The minimum frequency of light required for an electron to be emitted
What equation is used to determine the energy of a photon?
E=hf = hc/λ Energy = Plancks constant x frequency Energy = (PCx3x10^8)/ wavelength
Why does a photon need a minimum frequency to liberate an electron ?
Energy of a photon is determined by its frequency , the photons energy must be greater than the work function (energy needed to break bonds between electrons ) in order for an electron to be emitted
If a photon has a higher frequency than the threshold frequency , what would happen?
The electron will be liberated and the remaining energy will be converted into kinetic energy of the electron
If light is incident on a metal and photoelectric emission does not occur, what is the effect of increasing light intensity ?
1) If i is more intense there will be more photons incident on the metal each second
2) However each photon still carries the same energy as before
3) Therefore it still does not contain enough energy to liberate an electron
4) No effect
What is the photoelectric equation ?
Planck’s constant x frequency = work function + maximum kinetic energy of the photoelectrons
Define the work function
The energy required by an electron to overcome the metallic bond holding it in the metal
What is an electron volt?
The kinetic energy of an electron that has been accelerated from rest through a distance of 1 volt
How do you convert electron volts into joules and vice versa ?
eV x 1.6x10^19 = J
J / 1.6x10^19 = eV
How does a fluorescent tube work?
1) High voltage applied across mercury vapour accelerates fast moving electrons that collide with the mercury atoms
2) Mercury electrons are then excited then return to the ground state , releasing a UV photon
3) The tubes phosphorus coating absorbs the UV photons and its electrons are excited, they cascade down the energy levels releasing photons of visible light
What can be used as evidence for the discrete energy levels in atoms ?
Line emissions and absorption spectra as the lines appear at discrete points which show where a light photon of specific frequency and wavelength have been absorbed or emitted , this shows electrons can only absorb a specific amount of energy to be excited to the next discrete energy level
What is wave particle duality ?
All particles have both particle and wave properties , waves can have particle properties
e.g: light acts as a particle in the photoelectric effect and as a ave when deflected
