Glossary (Nuclear, Thermal and Astrophysics) AQA Physics A Unit 5A

The apparent magnitude a star would have if it were placed at a standard distance of 10 pc from Earth.
m – M = 5 log(d/10) where d is the distance in parsecs.

The number of emissions per second, measured in Becquerels.

The bright central region in an optical diffraction pattern caused by light entering a circular aperture.

Short-range, highly ionising radiation consisting of helium nuclei

The magnifying power of a refracting telescope, given by the ratio of the objective focal length to the eyepiece focal length.

The apparent brightness of a star expressed on the magnitude scale.
m = -2.5 log(b)

The average distance between the Earth and the Sun.

Unit of mass defined by 1/12 of the mass of a carbon-12 atom.

The number of particles in a mole of a substance.

Law stating that equal volumes of gases, at the same temperature and pressure, contain the same number of molecules.

The number of emissions per second that are detected due to radiation from the environment.

A series of emission or absorption lines in the visible spectrum of hydrogen. Resulting from electrons moving from the first excitation level (n=2) to higher levels.

Ionising radiation in the form of fast-moving electrons.

Two stars revolving around a common centre of mass.

The energy required to separate a nucleus into its constituent protons and neutrons.

The average energy required to remove each proton or neutron from a nucleus. The max (and most stable) is Iron (nucleon number 56, binding energy per nucleon 8.7 MeV).

A body that absorbs all wavelengths of electromagnetic radiation and can emit all wavelengths of EM radiation depending only on its temperature.

Highly dense matter around which gravity is so strong that the escape velocity exceeds the speed of light.

A decrease in observed wavelength radiation emitted by an object approaching an observer.

The ratio of the molar gas constant to the Avogadro constant.

Law stating that for a fixed mass of an ideal gas at constant temperature, the pressure of the gas is inversely proportional to its volume. pV is constant.

The amount of electromagnetic energy radiated per second per square metre.
b = L/(4πR^2) where L is luminosity and R is the distance of the object from the observer.

Type of reflecting telescope in which light rays are reflected by secondary mirror to focus behind the primary mirror.

An electronic light detector composed of many pixels, each of which builds up charge in proportion to the number of photons detected.

Law stating that for a fixed mass of an ideal gas at a constant pressure, the volume of the gas is proportional to its absolute temperature. V/T is constant.

An optical defect that causes light of different colours to be focused at different locations.

A spectrum of electromagnetic radiation distributed over a range of wavelengths without any spectral lines.

Rod of neutron absorbing material such as boron, which is used to slow the rate of fission in a nuclear reactor.

Isotropic radiation in the microwave region with a black body temperature of 2.7 K, believed to be a remnant of the big bang.

The minimum mass of fissionable material that can sustain a chain reaction.

The probability that a radioactive decay will take place in unit time.

Unit used to measure refractive power of a lens.

The apparent changing wavelength of radiation due to relative motion of the source and observer.
z = (λapp – λ)/λ = -v/c

Nuclear fuel that has had the proportion of its fissionable isotope artificially increased for example uranium that has had a proportion of U -235 increased

The decay of some large nuclei by splitting into two smaller nuclei, accompanied by the release of energy.

The formation of a larger nucleus by combining two smaller ones, accompanied by a release of energy.

Ionising radiation emitted during the decay of some radioisotopes, high energy electromagnetic radiation.

The time taken for half the nuclei in a sample of a radioisotope to decay, or the time taken for the activity of a radioactive source to drop by half.

A law stating that the redshifts of distant galaxies is proportional to their distance from the earth.

A gas that obeys boyle’s law under all conditions. A gas whose molecules are infinitely small and exert no force on each other except during collisions.

Fission of a nucleus caused by the absorption of an extra neutron.

The process of removing electrons from atoms.

The total energy radiated by a star each second, measured in watts

The difference between the mass of the nucleus and the total mass of its constituent nucleons.

Material used in a nuclear reactor to slow down neutrons without absorbing them, for example graphite.

The amount of substance a system contains in terms of the number of atoms there are in 12 g of carbon-12.

The highly dense remnant of a star after a supernova explosion, composed mainly of neutrons.

The distance at which two objects separated by 1 AU make an angle of 1 arcsecond (1/3600 degrees), equal to 3.26 light years or 3.09 x 10^13 km.

Law stating that for a fixed mass of an ideal gas at a constant volume, the pressure of the gas is proportional to its absolute temperature. p/T is constant.

The point at which rays of light which strike a convex lens parallel to the principal axis are brought together.

Rapidly rotating neutron star with strong radio emissions.

An astronomical object with a very large red shift and high luminosity, sometimes associated with the radio emission. Thought to be the bright nucleus of a distant active galaxy.

A way of assessing the resolving power of a telescope, given by θ=λ/d.

The increase in wavelength of radiation emitted by an object that is moving away from the observer.

A telescope that uses mirrors to capture and focus the light.

The telescope uses lenses to capture and focus the light. An arrangement of an objective lens and an eyepiece lens.

A measure of the ability of a telescope to distinguish between two astronomical features.

The radius of an imaginary sphere from the centre of a black hole at which the escape velocity is equal to the speed of light.
R = 2GM/c^2

The energy required to raise the temperature of a 1 kg mass of a substance by 1 K.

The energy required to change the state of a 1 kg mass of a substance with no change in temperature.

The type of star, as classified by its temperature. The sequence of spectral classes is OBAFGKM (Oh Be A Fine Girl Kiss Me).

The distortion of an image due to imperfections in the mirror or lens causing differing focal lengths.
The shorter the wavelength, the more precise the mirror has to be.

An astronomical object of known intrinsic brightness, for example a supernova, that is used to determine astronomical distances.

Relation that gives the total energy emitted per square metre per second from an object at a given temperature T to be proportional to T^4.
L = σAT^4

Relationship between temperature of a black body and the peak wavelength. λmaxT = 0.0029 m K

A low energy neutron which can be captured by an atomic nucleus to initiate fission. They have lost kinetic energy to heat.

This is sent around the reactor to remove heat. It has to be a fluid so it can be pumped around the reactor, and should have a large specific heat capacity. Water or carbon dioxide are often used.

The nuclear reactor is surrounded by a thick concrete case, which prevents radiation escaping.

The power received from an object per unit area at earth. This is the effective brightness of an object.
I = L/4πd^2

A plot of absolute magnitude of stars against their spectral class (surface temperature).
The vertical axis goes from 15 at the bottom to -10 at the top.
The horizontal axis goes in order of spectral class.
The sun is G2, +4.83.

On a large scale the universe is homogeneous (every part is the same as every other part) and isotropic (everything looks the same in every direction).