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What is the atom?
The smallest unit of a chemical element, composed of protons, neutrons, and electrons.
What is a proton?
A positively charged particle found in the nucleus of an atom, with a charge of +1.6 × 10−19 C.
What is a neutron?
A neutral particle found in the nucleus of an atom, with a mass nearly equal to that of a proton.
What is an electron?
A negatively charged particle that orbits the nucleus of an atom, with a charge of -1.6 × 10−19 C.
What is a nucleon?
Particles found in the nucleus of an atom, including protons and neutrons.
What is specific charge?
The charge-to-mass ratio of a particle, calculated by dividing its charge by its mass.
What is an isotope?
Atoms of the same element that have the same number of protons but different numbers of neutrons.
What is alpha decay?
A type of radioactive decay in which an atomic nucleus emits an alpha particle, decreasing the proton number by 2.
What is a beta-minus decay?
A type of radioactive decay in which a neutron is transformed into a proton, emitting an electron and an antineutrino.
What is a neutrino?
A nearly massless, neutral particle emitted during certain types of radioactive decay.
What is an antiparticle?
A particle that has the same mass as another particle but opposite charge and quantum numbers.
What is a photon?
A quantum of electromagnetic radiation, with energy proportional to its frequency.
What is annihilation?
The process in which a particle and its antiparticle collide, resulting in the conversion of their mass into energy, typically emitted as photons.
What is pair production?
The process where a photon transforms into a particle-antiparticle pair, requiring sufficient energy.
What is an exchange particle?
A particle that mediates interactions between other particles, responsible for forces like electromagnetic and nuclear forces.
What is a baryon?
A type of hadron consisting of three quarks, such as protons and neutrons.
What is a lepton?
A fundamental particle that does not experience the strong nuclear force, such as electrons and neutrinos.
What is strangeness?
A quantum number that indicates the presence of strange quarks in a particle, conserved in strong interactions.
What is the work function?
The minimum energy needed to remove an electron from the surface of a metal.
What is threshold frequency?
The minimum frequency of light required to eject electrons from a metal surface in the photoelectric effect.
What is quantum?
The smallest discrete quantity of any physical property, often referring to energy.
What does the strong nuclear force SNF do?
Keeps nuclei stable by counteracting the electrostatic force of repulsion between protons in the nucleus as they have the same charge. It only acts on nucleons and has a very short range: repulsive <0.5 fm, attractive 0.5<x<3 and negligible >3 fm.
What is an unstable nucleus?
A nucleus with too many protons, neutrons or both causing SNF to not be enough to keep them stable therefore it will decay in order to become stable. The type of decay depends on the amount of each nucleon in the nucleus.
What are four fundamental forces?
Gravity, electromagnetic, weak nuclear and strong nuclear
Strong nuclear: exchange particle? range? acts on?
Gluon, 3 fm, hadrons
Weak nuclear: exchange particle? range? acts on?
W boson, 10^-18, all particles
Electromagnetic: exchange particle? range? acts on?
Virtual photon, infinite, charged particles
Gravity: exchange particle? range? acts on?
Graviton, infinite, particles with mass
What is electron capture?
p+e- —> n+ve using a W+ boson
What is electron-proton collision?
p+e- —> n+ve using a W- boson
What is a hadron?
A type of particle that is formed from quarks and experience the strong nuclear force
What is the strangeness meson?
Kaons
Which properties must always be conserved in particle interactions?
Energy, momentum, charge, baryon number, electron lepton number, muon lepton number and strangeness (strong nuclear only)
What is the photoelectric effect?
Where photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it.
How is the photoelectric effect explained?
EM waves travel in discrete packets called photons which have an energy directly proportional to frequency. Each electron can absorb a single photon therefore a photoelectron is only emitted if the frequency is above the threshold frequency.
What is the stopping potential?
The potential difference you would need to apply across the metal to stop the photoelectrons with the maximum kinetic energy.
What is the photoelectric equation?
E = hf = Φ + Ek (max)
Why is stopping potential measured?
It allows you to find the maximum kinetic energy of the released photoelectrons as Ek (max) = eV, where V is the stopping potential and e is the charge on the electron. This is derived using energy = charge × voltage.
What is excitation?
When electrons in discrete energy levels gain energy from collisions with free electrons which can cause them to move up in energy level. It will then quickly return to its original energy level and therefore release the energy gained in the form of a photon
What is ionisation?
When electrons in discrete energy levels gain energy from collisions with free electrons which can cause them to be removed from the atom entirely. This occurs when the energy of the free electron is greater than the ionisation energy.
What is a practical use of excitation?
Fluorescent tubes are filled with mercury vapour across which a high voltage is applied. The voltage accelerates free electrons through the tube which collide with the mercury atoms causing them to become excited. When they de-excite they release photons most of which are in the UV range
What does the (phosphorus) fluorescent coating do?
It is on the inside of fluorescent tubes and absorbs the UV photons and therefore electrons in the atoms of the coating become excited and de-excite releasing photons of visible light.
What is an electron volt?
The energy gained by one electron when passing through a potential difference of 1 volt.
How do you convert from eV to joules and why?
energy = charge x voltage. So to convert from eV to joules multiply by 1.6 × 10^-19
How is a line spectrum created?
By passing the light from a fluorescent tube through a diffraction grating or prism
What is the evidence that shows why electrons can only transition between discrete energy levels?
As the line spectrum is not continuous but rather contains only discrete values of wavelength, the only photon energies emitted will correspond to these wavelengths
How is a line absorption spectrum created?
By passing white light through a cooled gas
What is a line absorption spectrum?
A continuous spectrum of all possible wavelengths of light with black lines at certain wavelengths.
What do the lines on a line absorption spectrum represent?
They represent the possible differences in energy levels as the atoms in the gas can only absorb photon of an energy equal to the exact difference between two energy levels
What is the equation for change in energy?
ΔE = E1 - E2
What is an example of light acting as a wave?
Diffraction and interference
What is an example of light acting as a particle?
Photoelectric effect
Why can electrons be shown as having both wave and particle properties?
The wave nature of electrons can be observed through electron diffraction as only waves can experience diffraction
What did De Broglie hypothesise?
If light was shown to have particle properties, then particles should also have wave-like properties
What is the De Brogile equation?
λ = h
What does the De Brogile equation show?
It shows how the amount of diffraction changes as a particle’s momentum changes
What happens to diffraction when momentum is increased?
The wavelength will decrease therefore the amount of diffraction decreases so the concentric rings of the interference pattern become closer together.
What happens to diffraction when momentum is decreased?
The wavelength will increase therefore the amount of diffraction increases so the concentric rings of the interference pattern become further apart.
What pattern does the electron diffraction interference form?
Concentric rings
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