Definitions for Physics A2 Flashcards
Absolute zero
With the temperature at which a system has a minimum internal energy equivalent to -273.15c
Acoustic impedance
Acoustic impedance Z is the product of the density of the substance and the speed of sound in that substance
Activity
The rate of decay or disintegration of nuclei in a radioactive sample
Amplitude
The maximum displacement of a particle from its equilibrium position
Angular displacement
The angle through which an object moves in a circle
Angular frequency
The rate of change of angle expressed in radian per second. angular frequency (ω) = 2π/T
Astronomical unit
The average distance of the Earth from the sun
Avogadro constant
The number of particles in one mole of any substance (6.02x10^23)
Big bang
An event that describes a very hot explosion from which space and time evolved - The beginning of the universe
Binding energy
The minimum external energy required to separate all the neutrons and protons of an nucleus
Black hole
A remnant of a massive star formed as a result of matter collapsing to a point (singularity) The density of a black hole is so intense that even light cannot escape from it
Boyles Law
The pressure exerted by fixed mass of gas is inversely proportional to to its volume, provided the temperature of the gas remains constant
Braking radiation
X-rays produced when electrons are decelerated
Capacitance
The ratio of charge stored by capacitor to the potential difference across it
Carbon dating
A technique used to date relics of using the carbon-14 isotope
Centripetal force
The net force acting on an object moving in a circle; it is always directed towards the centre of the circle
Chain reaction
And exponential growth of a fission reaction caused by the increasing flux of neutrons causing fission
Chandrasekhar limit
The maximum mass of the white dwarf - about 1.4 solar masses
Characteristic radiation
Very intense x-rays produced in an x-ray tube having specific wavelengths that depend on the target metal
Charles’s law
The volume occupied by gas at constant pressure is directly proportional to its thermodynamic temperature (absolute)
Closed system
A system of interacting objects where there are no external forces
Closed universe
And model of the universe in which gravitational force is strong enough to hold its expansion and reverse the process towards a big crunch
Collimated beam
A parallel sided beam of radiation
Collimator
A device for producing a parallel beam of radiation
Compton scattering
An interaction between an x-ray photon and an electron in which the photos are scattered with a longer wavelength
Computerised axial tomography
A technique where x-rays are used to image slices of the body in order to produce a computerised 3-D image
Conservation of momentum
In a closed system, when bodies interact, the total momentum in any specified direction remains constant
Contrast
In a high contrast image there is a big difference in brightness between bright and dark areas
Contrast media
Material such as Bury and that is the absorb x-rays. Contrast medium is used to reveal the outlines or edges of soft tissues in an x-ray image
Control rods
Rods of a neutron absorbing material are used to reduce the rate of a nuclear chain reaction
Coolant
A substance used to transfer thermal energy from the core of a nuclear reactor
Cosmic microwave background radiation
Electromagnetic radiation in the microwave region of the spectrum that corresponds to a temperature of the universe of 2.7 K
Cosmological principle
The principal states that the universe has the same large-scale structure when observed from any point in the universe
Coulombs law
Any two point charges exert an electrical force on each other that is proportional to the product of the charges and inversely proportional to the square of the distance between them
Count Rate
The number of particles (beta or alpha) or gamma-ray photons detected per unit time by Geiger-Müller tube. Can’t rate is always a fraction of the activity of a sample
Critical density
The density of the universe that will give rise to a flat universe, given by the equation 3Ho^2/8πG
Damped
Describes an oscillary motion with the amplitude decreases with the time due to energy losses
Dark energy
A form of energy thinly distributed throughout the universe which may be causing the expansion of the universe to accelerate
Dark matter
Matter that emits or reflects little electromagnetic radiation, making it difficult to detect
Decay constant
The constant λ for an isotope that appears in the equation A=λN. It is equal to the probability of an isotope decaying per unit time interval
