OCR PHYSICS A- All of it!

Newton's law of gravitation

the fore between two point masses is directly proportional to the product of the masses and inversely proportional to the square of the separation of the distance between them F=(-GMm)/r^2

Brownian motion

the continuous random motion of small particles suspended in a fluid, visible under a microscope

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

absorption coefficient

a measure of the absorption of X-rays by a substance, also known as the attenuation unit m ^ - 1

absorption line spectrum

a set of frequencies of electromagnetic 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. (dark lines on colour)

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 feild, symbol g

acoustic impedance

the product of the density (p) of a substance and the speed, c, of ultrasound in that substance - symbol, Z, SI unit kgm^-2s^-1

acoustic matching (or impedance matching)

The use of two substances with similar acoustic impedance to minimise reflection of ultrasound at the bounday etween them

activity

the rate at which nuclei decay or disintegrate in a radioactive source, measured in Becquerels (Bq) or decays per second

alpha radiation

ionising radiation consisting of particles comprising two protons and two neutrons (a helium nucleus), with a charge of +2e

air resistance

the drag or resistive force experienced by objects moving through the air

ammeter

a device used to measure electric current - it must be place in series and ideally have zero resistance

amount of substance

a measure of the amount of matter in moles

ampere

the base SI unit of electric current, symbol A, defined as the current flowing in two parallel wires in a vacuum 1m apart such that there is an attractive force of 2.0*10^-7 N per meter length of meter between the

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 the 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 the frequency and 2pi

angular velocity

the rate of change of angle for an object moving in a circular path, symbol w,

anion

a negatively charged ion, one which is attracted to the anode

antiparallel (vectors)

in the same line but in opposite directions

antiparticle

the antimatter counterpart with an opposite charge to the particle and exactly the same rest mass

antiphase

particles oscillation completely out of step with one another (one reaches its maximum when the other reads its minimum.

aphelion

the furthest point from the sun in an orbit

Archimedes' Principle

the upthrust on an object in a fluid is equal to the weight of the fluid that it has replaced

arcminuite

a minute of arc; 1degree is 60 arcminutes

arcsecond

a second of arc; 1 arcminuite is 60 arc seconds

astronomical unit

the mean distance from the earth to the sun 150 mil km

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 (Z)

attenuation

the decrease in the intensity of electromagnetic radiation as it passes through matter and/or space

attenuation coefficient

a measure of absorption of X-ray photons by a substance, also know as the absorption coefficient - SI unit m^-1

average speed

the rate of change in distance calculated over a complete journey

average velocity

the change in the displacement ∆s for a journey divided by the time taken ∆t; ∆s/∆t

Avogadro constant

6.02*10^23, the number of atoms in 0.012kg (12g) of carbon-12; symbol N(a)

background radiation

the radiation emitted by the surroundings, which must be measured before radiation produced in an experiment can usually be measured

baryon

any hadron made with a combination of three quarks

base unit

one of seven units that form the building blocks of the SI measurement system
metre
kilogram
second
ampere
kelvin
mole
candela

battery

a collection of cells that transfers chemical energy into electrical energy

Becquerel

a unit of activity - one Becquerel is an activity of one decay per second

beta decay

a neutron in an unstable nucleus decays into a proton, an electron, ad an electron antineutrino (beta-minus decay), or a proton to a neutron, a positron, and an electron neutrino (beta plus decay)

beta radiation

ionising radiation consisting of fast-moving electrons (beta-minus) or (beta-plus) emitted from an unstable nuclei, with a charge of -e or +e, respectively

big bang

the theory that at a moment in the past all the matter in the 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 an neutrons

binding energy per nucleon

the binding energy divided by the number of protons and neutrons in the nucleus; the greater the binding energy per nucleon, the more tightly bound are the nucleons within the nucleus

black body

an idealised object that absorbs all the electromagnetic radiation incident on it and, when in thermal equilibrium, emits a characteristic distribution 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 that in order to escape it an object would be need to be travelling at an escape velocity greater than the speed of light, and therefore nothing, not even photons 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 absorption lines in its spectrum will be blue shifted, that is, moved towards the blue end of the spectrum

boltmann constant

the molar gas constant, R, divided by the Avogadro constant N(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 in inversely proportional to its volume, provided that the mass of gas and the temperature do not vary

braking distance

distance travelled by a vehicle from the time the brakes are applied until the vehicle stops

breaking strength

the stress value at the point of fracture, calculated by dividing the breaking force by the cross-sectional area

brittle

property of a material that does not show plastic deformation and deforms very little (if at all) under high stress

capacitance

the charge stored per unit potential difference across a capacitor

capacitor

a component that stores charge, consisting of two plates separated by an insulator (dielectric)

carbon dating

a method for determining the age of organic material of interest and similar living material

cathode

a negatively charged electrode

cation

a positively charged ion, one which is attracted to a cathode

cell

a device that transfers chemical energy into electrical energy

Celsius scale

a temperature scale with 100 degrees between the freezing point and the boiling point of pure water (at atmospheric pressure 1.01*10^3 Pa) 0 degrees and 100 degrees

centre of gravity

an imaginary point at which the entire weight of an object appears to act

centre of mass

a point through which any externally applied force produces straight-line motion but no rotation

centripetal acceleration

the acceleration of any object travelling in a circular path at constant speed, which always acts towards he centre of the circle

centripetal force

a force that keeps a body moving with constant speed in a circular path

chain reaction

a reaction in which the neutrons from an earlier fission stage are responsible for further fusion reactions leading to an exponential growth in the rate of the reactions

Chandrasekhar limit

the mass of a star's core beneath which the electron degeneracy pressure is sufficient to prevent gravitational collapse, 1.44soloarmasses

charge carrier

a particle with the charge that moves through a material to form an electric current - for example, an electron in a metal wire

closed system

an isolated system that has no interaction with its surroundings

cloud chamber

a detector of ionising radiation consisting of a chamber filled with air saturated with vapour at a very low temperature so that droplets of liquid condense around ionised particles left along the path of radiation

coherence

two wave sources or waves that are coherent have a constant phase difference

collimator

part of a gamma camera, a honeycomb of long, thin tubes made from lead that absorbs any photons arriving at an angle to the axis of the tubes so that a clear picture is obtained

comet

a small, irregular body made of ice, dust and small pieces of rock (an often highly eccentric elliptical) orbit around the sun - as they approach the sun, some comets develop spectacular tails

component

one of the two perpendicular vectors obtained by resolving a vector

compression(not waves)

the decrease in length of an object when a compressive force is exerted on it

compression (waves)

a moving region in which the medium is denser or has higher pressure than the surrounding medium

compressive deformation

a change in the shape of an object due to compressive forces

compressive force

two or more forces together that reduce the length or volume of an object

conical pendulum

a simple pendulum that, instead of swinging back and forth, rotates in a horizontal circle at constant speed

conservation of charge

a conservation law which states that electric charge can neither be created nor destroyed - the total charge in any interaction must be the same before and after the interaction

constant speed

motion in which the distance travelled per unit time stays the same

constant velocity

motion in which the change in displacement per unit time stays the same

constructive interference

superposition of two waves in phase so that the resultant wave that greater amplitude than the original waves

continuous spectrum

a spectrum in which all visible frequencies or wavelengths are present (a heated solid metal such as a filament lamp will produce this type of spectrum)

control rods

rods made of a material whose nuclei readily absorb neutrons (commonly boron or cadmium), which can be moved into or out of a reactor core to ensure that exactly one slow neutron survives per fission reaction or to completely stop the fission reaction

conventional current

a model used to describe electric current in a circuit - conventional current travels from positive to negative - it is the direction in which positive charges would travel

coolant

a substance that removes the thermal energy produced from reactions within a fission reactor

corrected count rate

the radiation count rate measured in an experiment minus the background count rate

cosmological principle

the assumption that, when viewed on a large enough scale, the Universe is homogeneous and isotropic, and the laws of physics are universal

coulomb

the derived SI unit of electrical charge, symbol C; 1 coulomb of electric charge passes a point in one second when there is an electric current of one ampere

Coulomb's law

any two point charges exert and electrostatic (electrical) force on each other directly proportional to the product of their charges and inversely proportional to the square of their separation

couple

a pair of equal and opposite forces acting on a body but not in the same straight line

coupling gel

a gel with acoustic impedance similar to that of skin smeared onto the transducer and the patient's skin before an ultrasound scan in order to fill air gaps and ensure that almost all the ultrasound enters the patient's body

critical angle

the angle of incidence at the boundary between two media that will produce an angle of refraction of 90°

crystallography

a method for determining the structure of a substance by studying the interference patters produced by waves passing through a crystal of the substance

damping

an oscillation is damped when an external force that acts on the oscillator has the effect of reducing the amplitude of its oscillations

dark energy

a hypothetical form of energy that fills all of space and would explain the acceleraiton of the universe

dark matter

a hypothetical form of matter spread throughout the galaxy that neither emits nor absorbs light - it could explain the differences between the predicted and observed velocities of stars in galaxies

daughter nucleus

a new nucleus formed following a radioactive decay