Quantum Phenomena Flashcards
What is the photoelectric effect?
When light (Electromagnetic radiation) is shone on a metal surface, the photons from the light will be absorbed by the electrons. If the threshold frequency is exceeded, the electrons will be emitted off the surface of the metal.
What is the threshold frequency?
The minimum value of frequency for photoelectrons to be emitted off the surface of a metal/for the photoelectric effect to take place.
What happens when the frequency of light is increased?
The photons will have a higher frequency, therefore the photoelectrons emitted will have a larger kinetic energy/move at faster speeds.
What happens when the intensity of light is increased?
More photons will be shone on the surface of the metal, therefore more photoelectrons will be emitted per second.
What is the work function?
The minimum energy required for photoelectrons to be emitted off the surface of a metal/for the photoelectric effect to take place.
What is the stopping potential?
The potential difference required to apply across the metal to stop the photoelectrons with maximum kinetic energy.
What is the stopping potential equation?
EK = eV
Where:
V = Stopping potential
e = Charge of an electron
What is excitation?
When an electron gains energy from collisions with free electrons, it moves up an energy level. When it de-excites to its original energy level, it releases energy gained as a photon.
What is Ionisation and Ionisation energy?
When an electron gains energy through collisions with free electrons, it can be completely removed from the atom. This only happens when the ionisation energy is reached - energy required to remove an electron from an atom.
Fluorescent tubes
A fluorescent tube is filled with mercury vapour, coated with a phosphorous (fluorescent) coating, with a high voltage applied across it.
- Voltage accelerates free electrons across the tube.
- Mercury atoms become ionised (releasing more free electrons) and excited. When they de-excite, they release UV photons.
- Phosphorous coating absorbs these UV photons, and become excited. When they de-excite, they emit photons of visible light.
What is an electron volt?
Energy gained by one electron when passing through a potential difference of 1V.
What is the line emission spectra?
When light from a fluorescent tube is shone through a prism or diffraction grating, it forms a line spectrum. Each line corresponds to a particular wavelength. This is evidence that electrons exist in discrete energy levels.
What is the line absorption spectrum?
When passing white light through a cooled gas, it shows a continuous spectrum of all possible wavelengths of light, with black lines at certain wavelengths.
Proof of wave-particle duality of light
Wave-like properties: diffraction and interference, Young’s double slit experiment.
Particle-like properties: light is emitted in discrete packets called photons, the photoelectric effect.
Proof of wave-particle duality of electrons
Wave-like properties: de Broglie’s wavelength, electron diffraction.
Particle-like properties: the existence of electrons in an atom, cathode ray experiment by J.J. Thomson. When a magnetic field was applied, the charge bent away from the magnet - some sort of negative charge was acting.
