Particles and Waves Glossary

Click on the read more to get a glossary of the terms for this unit. I will try to update it as I think of more words that I need to add, or try the quizlet for revision

absolute refractive indexthe absolute refractive index (or just the refractive index), n , of a medium is the ratio of the speed of light in a vacuum to the speed of light in the material. (also the ratio of the wavelength of light in a vacuum to the wavelength of light in the medium)
angle of incidencethe angle between the incident ray and the normal.
angle of refractionthe angle between the refracted ray and the normal.
atomic mass units (u)by definition one twelfth of the mass of a carbon-12 nucleus.
atomic numberthe number of protons in an atomic nucleus. It is this number that determines the element and its properties.
binding energythe energy needed to split a nucleus into its separate nucleons (not on the CfE Higher course)
chain reactionwhen a nucleus undergoes fission it releases neutrons that can go on to cause further fission reactions by interactions with other nuclei. If there is a sufficient concentration of suitable nuclei, the process becomes self-sustaining.
coherent wavescoherent waves are waves that have the same frequency, speed and have a constant phase relationship.
collimatorpart of a spectrometer that is used to produce a parallel beam of light.
constructive interferencewhen waves arrive at a point in phase or crest meets a crest and trough meets a trough resulting in a wave of larger amplitude than the individual waves.
critical anglethe angle above which total internal reflections occurs. Or, the maximum value of the angle between the normal and the ray in glass, θ glass, for which refraction can occur.
destructive interferencewhen waves arrive at a point in out of phase or crest meets a trough resulting in a wave of smaller amplitudeas the waves cancel out.
diffractionan effect that causes waves to bend as they go past the end of an obstacle or through a small gap in a barrier.
dispersionthe process of splitting up light into its constituent colours, this can be done with a prism and white light.
electromagnetic wavesthe spectrum of waves that includes radio, visible light, X-rays etc which all have no mass and travel at the speed of light in a vacuum.
excited stateany atomic energy level higher than the ground state.
ferromagneticmaterials in which the magnetic fields of the atoms line up parallel to each other in regions known as magnetic domains.
fissionthe splitting of a large atomic nucleus into smaller fragments, with the resultant release of excess energy.
gold leaf electroscopedevice used to measure small amounts of charge.
gratinga transparent slide of glass or plastic that has a very large number of equally spaced grooves machined on to its surface. Each groove acts as a source for coherent beams of light.
ground statethe lowest energy level of an atom where an electron has the lowest energy level.
induced fissionthe deliberate splitting of a large nucleus caused by the collision of the nucleus with a neutron.
interferencea phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude.
ionisation levelthe energy level at which an electron can break free from an atom.
irradiancethe power per unit area of radiation incident on a surface.
isotopesdifferent forms of the same element. The isotopes of an element contain the same number of protons but have different numbers of neutrons. (Many isotopes are unstable and can emit nuclear radiation)
line absorption spectruma spectrum that consists of narrow dark lines across an otherwise continuous spectrum.
line emission spectruma spectrum consisting of narrow lines of light, the position of which depend on the substances producing the light.
magnetic domainsregions in a ferromagnetic material where the atoms are aligned with their magnetic fields parallel to each other.
magnetic fielda magnetic field is a region in which a moving charge experiences a magnetic force.
magnetic polesone way of describing the magnetic effect, especially with permanent magnets. There are two types of magnetic poles - north and south. Opposite poles attract, like poles repel.
mass defect (do not confuse with mass difference)the difference between the mass of a nucleus and the total mass of an  equal number of individual nucleons.
mass differencethe difference in mass between the reactants and products in a nuclear reaction. The resulting mass difference is converted to energy according to the equation E=mc 2 .
mass numberthe total number of nucleons (protons and neutrons) in the nucleus of an atom.
monochromaticradiation consisting of a single frequency.
monochromatic lightlight of one wavelength (and therefore one colour)
normala line drawn at right angles to a surface or the boundary between two different media
nucleonthe general term for protons and neutrons (contained in the nucleus).
nuclidethe nuclei of one particular isotope. These nuclei all have the same atomic number and mass number.
path differencethe difference in path lengths of two sets of waves.
phasedenotes the particular point in the cycle of a waveform.
photocathodethe terminal from which electrons will be emitted due to the photoelectric effect.
photoelectric effectthe emission of electrons from a metal due to the effect of electromagnetic radiation.
photoelectronsfree electrons produced by the photoelectric effect
photoemissionthe emission of electrons from a material caused by light shining on it.
photonthe particle of electromagnetic radiation.
potential differencethe potential difference between two points is a measure of the work done in moving one coulomb of charge between the two points.
principle of reversibilitythe principle of reversibility states that a ray of light will follow the same path in the opposite direction when it is reversed.
prisma prism is a transparent optical element with flat, polished surfaces that refract light. A dispersive prism can be used to break light up into its constituent spectral colours.
quantaa "packet" certain amount, often referring to the energy of photons.
radioactive decay seriesa chain of radioactive decays as a radioactive element changes to eventually become a stable, non-radioactive element.
radioisotopeshort for radioactive isotope.
radionuclideshort for radioactive nuclide.
refractionrefraction occurs when a wave goes from one medium into another. When a wave is refracted, its speed and wavelength change; its frequency remains constant; its direction sometimes changes.
spectrometeran instrument that can make precise measurements of the spectra produced by different light sources.
spontaneous fissionthe random splitting of a large atomic nucleus due to the internal processes within the nucleus. (it does not require neutrons to cause the reaction and so is not of use in a nuclear reactor).
stopping potentialthe minimum voltage required to reduce photoelectric current to zero.
telescopethe part of a spectrometer through which the spectrum is viewed.
threshold frequencythe minimum frequency of electromagnetic radiation that will cause photoemission for a particular substance.
total internal reflectionwhen a ray of light travelling in a more dense substance meets a boundary with a less dense substance at an angle greater than the critical angle, the ray is not refracted but is all reflected inside the more dense substance.
turntablethe stage or platform of a spectrometer on which the grating or prism sits. The turntable has an angular scale on it to allow measurements to be made.
work functionthe minimum energy required to cause photoemission from a substance.
February 2019