Quantum Physics Flashcards
(21 cards)
What does the term Coherent mean?
Waves of the same type and the same frequency/wavelength which maintain a constant phase difference (Amplitudes do not have to equal)
What does the term Interference mean?
When Coherent wave sources meet and constructive or destructive interference occurs forming a pattern of equally spaced, bright and dark fringes.
What does the term Path Difference mean?
The difference in the distances two waves have travelled. For constructive interference path difference = nλ; for destructive interference = n+(1/2)λ
What does Diffraction Effects mean?
Spreading out of waves as they pass through an opening or past the edge of an obstruction. Maximum diffraction occurs when λ = gap size
What is a Photon?
A packet or quantum of electromagnetic energy (quanta = plural)
What does the term Photoelectric Effect mean?
The emission of electrons from the surface of a metal by absorbing photons (whose energy is greater than the work function)
What does the term Photon Energy mean?
The energy of a quantum of light (photon) is a defined amount and depends on the frequency and Planck’s constant.
* E = hf, (h = 6.63x10^-34)
* E = hc/λ
What does the term Work Function mean?
The minimum amount of energy required to just liberate an electron from the surface of a metal and allow it to escape to an infinite distance from the metal.
What is an Electron-Volt (eV)?
A unit of energy and equivalent to the energy gained or lost by an electron moved through a potential difference of 1 volt.
1eV = 1.6x10^-19 J
What is meant by the term
Energy Levels?
An electron has a fixed amount of energy in each orbit (closest to the nucleus = least and further = most energy). An electron an infinite distance from the nucleus has zero energy. The energy of electrons in orbit are therefore negative.
What is meant by the term
Ground State?
When all electrons in an atom have their lowest possible energy the atom is considered to be in the ground state.
What is meant by the term
Excitation?
An electron absorbs a photon of energy and moves to a higher energy level.
What is meant by the term
Relaxation?
An electron moves from an excited state to a lower level, emitting a photon of energy.
What is meant by the term
LASER?
Light Amplification by Stimulated Emission of Radiation. A monochromatic, coherent, high intensity source of optical, UV or IR radiation.
What is meant by the term
Population Inversion?
When the number of electrons within a group of atoms exist in greater numbers in an excited state than in the ground state.
What is meant by the term
Metastable State?
An Energy level with a longer lifetime than a normal state
What is meant by the term
Stimulated Emission?
A stimulating photon of hf = ΔE causes an electron to relax to the ground state and emit a photon with the same phase, frequency, polarisation and direction.
What is meant by the term
Wave-Particle Duality?
All matter exhibits both wave and particle properties and can be viewed in one way or another but not both simultaneously.
What is meant by the term
Wave model?
The wave nature of a phenomenom with observable effects such as diffraction, interference and polarisation (as exhibited by E-M waves).
What is meant by the term
Particle/Photon model?
The particle nature of a phenomenom where a particle exhibits momentum or exists as a ‘packet’ of energy such as a quantum.
What is meant by the term
Electron Diffraction?
If a beam of electrons is passed through a graphite crystal, a diffraction pattern of light and dark concentric rings is observed.
