3.2.2 Electromagnetic Radiation and Quantum Phenonmena Flashcards
What is threshold frequency?
The minimum frequency required of an EM photon to remove an electron from the surface of a metal
Define work function
The minimum energy required of a photon to release an electron from the surface of the metal
Define stopping potential
The potential difference required to stop photoelectrons emission.
What is the equation for stopping potential?
Vs = Ek(max) / e
What can cause excitation?
An electron can absorb a single photon with an exact energy or a free electron could collide with the orbital electron transferring some of its energy.
What are the two ways an electron can de excite (to its original energy level) ?
One direct transition in energy levels emitting one photon or cascading down multiple energy levels emitting multiple photons.
All photons have energy equal to the change in energy level
Define ionisation
When an electron gains enough energy to be removed from the atom.
Define ionisation energy
The amount of energy required to remove an electron from an atom starting at the ground state.
How do fluorescent tubes work?
Electrons are accelerated to high speeds across the tube by a high voltage.
They will pass through mercury vapour in the tube and so collide with mercury atoms. This causes excitation and then de excitation in the mercury atoms which results in the emission of UV photons.
These photons are then absorbed by phosphor atoms coating the tube causing excitation and de excitation resulting in the emission of visible light photons.
How do you convert from eV to J?
- 1.6*10^-19
How do light emission spectra work?
Gas discharge tubes are used to excite gas and so shortly after de excite.
This will result in the emission of photons which can be split by a prism to produce a line emission spectra of bright lines against a black background
How do line emission spectra support the idea of discrete energy levels?
There are only certain wavelengths seen on the spectra. Therefore the photons must have certain energies and so the de excitation that produced them can only have occurred between specific energy levels.
Give examples of electrons demonstrating wave like properties
Electron diffraction and refraction
Give examples of electrons demonstrating particle like properties
The photoelectric effect and excitation
Define diffraction
The spreading out of waves as they pass through a gap the size of which is the same magnitude as the wavelength of the incident wave.
What is the effect of decreasing the gap size on diffraction?
It will result in a greater diffraction effect
What is the result of decreasing the wavelength on diffraction?
It will cause a smaller diffraction effect
Why can’t diffraction occur with larger particles?
Large particles have an incredibly small de brogile wavelength which demands a gap impossible to interact with
What does the symbol eVs represent?
The maximum kinetic energy of a photoelectron
Define an electron volt.
The energy gained by an electron travelling through a pd of 1V
