Definitions Flashcards
OCR A-level physics definitions on everything
absolute scale of temperature
a scale for measuring temperature based on absolute zero and the triple point of pure water, with gradations equal in size to those of the Celsius scale
unit: kelvin (K)
absolute zero
the lowest possible temperature, the temperature at which substances have minimum internal energy
absorption coefficient (attenuation coefficient)
a measure of the absorption of X-ray photons by a substance.
unit: m-1
absorption line spectrum
a set of specific frequencies of EM radiation, visible as dark lines in an otherwise continuous spectrum on spectroscopy.
they are absorbed by atoms as their electrons are excited between energy states by absorbing the corresponding amount of energy in the form of photons- every element has a characteristic line spectrum.
acceleration
the rate of change of velocity,
a vector quantity
acceleration of free fall
the rate of change of velocity of an object falling in a gravitational field
symbol g 9.81ms-2
acoustic impedance
the product of the density (p-row) of a substance and the speed (c-speed of light) of ultrasound in that substance -
symbol Z
unit kg m^-2 s^-1
acoustic matching (or impedance matching)
the idea of two substances with similar acoustic impedance to minimise reflection of ultrasound at the boundary between them
activity
the rate at which nuclei decay or disintegrate in a radioactive source, measured in bequerels (Bq) or decays per second
alpha radiation
ionising radiation consisting of particles compromising two protons and two neutrons (a helium nucleus)
charge: +2e
air resistance
the drag or resistive force experienced by objects moving through air
ammeter
a device used ri measure electric current - it must ensure placed in series and ideally have zero resistance
amount of substance
a measure of the amount is matte in moles
ampere
the Base SI unit is electrical current, symbol A, defined as the current flowing in two parallel wires in a vacuum 1 my apartment such that there is an attractive force of 2.0 × 10^-7 per metre length of wore between them.
amplitude (waves)
the maximum displacement from the equilibrium position (can be positive or negative )
angle of incidence
the angle between the direction of travel of an incident wave and the normal at a boundary between two media
angle of reflection
the angle between the direction of travel of a reflected wave and the normal at a boundary between two media
angular frequency
a quantity used in oscillatory motion - equal to the product of frequency (f) and 2 (pie)
angular velocity
the rate kf cha very of an angle for am object moving circular path - symbol (w)
anion
a negatively charged ion, one which is attracted to am anode
annihilation
the complete destruction of a particle and it’s antiparticle in an interaction that releases energy in the form of an identical photons
anode
a positively charged electrode
antiparallel (vectors)
in the same line but opposite directions
antiparticle
the antimatter counterpart of a particle, with the opposite charge to the particle ( if the particle has charge) and exactly the same rest mass as the particle
antiphase
particles oscillating completely out of step with each other (one reaches its maximum negative displacement) are in antiphase
aphelion
the furthest point from the sun in an orbit
Archimedes’ principle
the upthrust on an object in an fluid is equal to the weight of fluid it displaces
archminute
a minute of arc; 1 degrees = 60 arcminutes
archsecond
a second of arc; 1 arcminute = 60 arcseconds
astronomical unit
the mean distance from the Earth to the sun, I.e 150 million km
or
1.50 × 10^11 m
atomic mass unit
one atomic mass unit (1 u) is one - twelfth the mass of a neutral carbon -12 atom
atomic number
the number of protons in a nucleus- symbol Z
attenuation
the decrease in the intensity of electromagnetism radiation as it passes through matter and/or space
attenuation coefficient
a measure of the absorption of x- ray photons by a substance, also known as absorption coefficient-
SI unit m^-1
average speed
the rate of change in distance calculated over a complete journey
average velocity
the change in displacement for a journey divided by the time taken
velocity = displacement/time
avogadro constant
6.02 ×10^23
the number of atoms in 0.012 kg (12g) of carbon -12;
symbol N (subscripted)A
background radiation
the radiation emitted by the surroundings, which must be measured before radiation produced in an experiment can usefully be measured
baryon
any hadron made with a combination of three quarks
base unit
one of seven units that for now the building blocks of the SI measurement system
battery
a collection of cells that transfers chemical energy into electrical energy
bequerel
a unit of activity - one bequerel is an activity of one decay per second
beta decay
a neutron in an unstable nucleus decays Into a proton, an electron, and an electron antineutrino (ß- decay), or a proton into a neutron, a positron, and an electronic neutrion (ß+ decay)
beta radiation
ionising radiation consisting of fast- moving electrons (ß-) or (ß+) emitted from unstable nuclei, with a charge of -e or +e respectively
big Bang
the theory that at a moment in the past all matters in universe was contained in a singularity (a single point), the beginning of space and time, that expanded rapidly outwards
binding energy
the minimum energy required to completely separate a nucleus into its constituent protons and neutrons
binding energy per nucleon
the binding energy divided by the number of protons and electronic in the nucleus; the greater the binding energy per nucleon, the more tightly bound are the nucleon within the nucleus
black body
an idealised object that absorbs all the electromagnetic radiation incident on it and, when in the thermal equilibrium, emits a characteristic disribution of wavelengths at a specific temperature
black hole
the remnant core of a massive star after it has gone supernova and the core has collapsed so far in that in order tracking escape it an object would need an escape velocity greater than he speed of light, and therefore nothing, not even protons, can escape
blue shift
the shortening of observed wavelength that occurs when a wave source is moving towards the observer - in astronomy, if a galaxy Is moving towards the Earth, the alsor5libes in its spectrum will be blue shifted, that is, moved towards the blue end of the spectrum
Boltzmann constant
the molar gas constant (R) divided by the Avogadro constant (N (subscripted) a), a constant that relates the mean kinetic energy of the atoms or molecules in a gas to the gas temperature - symbol (K)
Boyle’s law
the pressure of an ideal gas is inversely proportional to its volume, provided that the mass of gas and the temperature do not vary
braking distance
distance travelled vt a vehicle from the tune brakes are applied until the vehicle stops
breaking strength
the stress value at the point of fracture, calculated by dividing the braking fore by the cross-sectional area
brittle
property of material that does not show plastic deformation and deforms very little (if at all) under high stress
Brownian motion
the continuous random motion of small particles suspended in a fluid, visible under a microscope.
