Quantum Phenomena Flashcards
What type of waves are electromagnetic waves?
Transverse - direction is perpendicular to energy transferred
What phenomena can be used to show how light behaves as a particle
The photoelectric effect
Describe the photoelectric effect? (3)
When light above a particular frequency is shone on the surface of a metal,
the electrons absorb the photons energy entirely, exciting them to higher energy levels
they are ionised from the surface of the metal and are emitted as photo electrons
What is threshold frequency
The minimum frequency of light incident on a metals surface that when absorbed, electrons are ionised from a metals surface
Why does a photon require to have a minimum frequency to liberat e an electron
Energy of a photon in determined by its frequency
as E = hF
The photons energy must be greater there the metals work function in order for an electron to be ionised
What does increasing light intensity have on the photo-electric effect
More intense = More photons incident per second as more electrons absorb more photons ,given that the frequency of light is above the threshold, so each photon has more energy then the work function, as more electrons absorb more photons
Energy of each photon doesnt change, so if energy is less then the work function then no change in photoelectric emissions
What is the work function equation
hf = Work Function + Kinetic Energy Max
Define work function
The energy required to ionise an electron from the metals surface
What is an electron volt
The kinetic energy of an electron that has accelerated from rest to a potential difference of 1v
How does a fluorescent tube work?
High voltage applied across mercury vapour
Accelerates fast moving free electrons which collide with the mercury atoms
Mercury electrons are excited and then returned to their ground state releasing a uv photon
The tubes phosphorus coating absorbs the uv photon and its electrons are excited
The elections cascades down their energy levels emitted visible light photons
What can be used as evidence for the discrete energy levels in atoms
Lien emission absorption spectra
Absorption Lines appear at discrete points which show where a photon of specific frequency and wave length has been
This shows electrons can only absorb exact amounts of energy
Reinforced by an emission spectra lines, of photons which are released as electrons dexcite
What is wave Particle duality
All particles have both particle and wave properties
and vice versa
How does the photoelectric effect prove wave particle duality (6)
Electrons are emitted without noticeable decay
If wave theory time would elapse while an electron gains sufficent energy to be ionised
There is a threshold frequency
Electrons have to gain an exact amounts above the work function of the metal of energy to cause emission and photon energy and frequency are related. If wave theory then this would mean that there would be photoelectric emission when any wave is incident.
Intensity of radiation incident is directly proportional to the number of photo electrons released
Each Photon only can liberate 1 electron.
What happens if an electrons absorbs a photon not equal to an energy gap between the sub shell it is in and a futher sub shell.
Electron doesn’t excite, as photons are absorbed entirely or not at all
Electron then will release the photon back.
