Ocr A Physics Definitions Page 1 & 2

Front 1

Absolute scale of temperature

Back 1

A scale for measuring temperature based on absolute zero and the triple point of pure water; gradiations equal in size to those of celsius. Unit kelvin (K)

Front 2

Absolute Zero

Back 2

The lowest possible temperature; the temperature at which substances have minimum internal energy

Front 3

Absorption co-efficient

Back 3

A measure of the absorption of X-ray photons absorbed by a substance. SI unit m^-1

Hint 3

Also called the attenuation co-efficient

Front 4

Absorption Line Spectrum

Back 4

A set of specific 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 photons with a corresponding amount of energy in the form of photons.

Hint 4

Visible as dark lines in what would otherwise be a spectrum in which all visible frequencies or wavelengths are present.

Every element has a characteristic line spectrum

Front 5

Acceleration

Back 5

The rate of change of velocity; SI unit ms^-2

Hint 5

A vector quantity

Front 6

Acceleration of free fall

Back 6

The rate of change of velocity of an object falling in a gravitational field; symbol g

Front 7

Vector quantity

Back 7

A quantity which has both direction and magnitude

Front 8

Scalar quantity

Back 8

A quantity with magnitude but not direction

Front 9

Energy

Back 9

The capacity to do work

Hint 9

W=Fx= Energy transferred

Front 10

Principle of conservation of energy

Back 10

The total energy of a closed system remains constant; energy cannot be created or destroyed, but it can only be transferred from one form to another

Hint 10

Energy is a scalar quantity

Front 11

Acoustic impedance

Back 11

The product of density p of a substance and the speed c of ultrasound in that substance.

Hint 11

Symbol Z, SI unit kgms^-2s^-1

Front 12

Acoustic matching

Back 12

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

Hint 12

Impedance matching

Front 13

Activity

Back 13

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

Front 14

Alpha radiation

Back 14

Ionising radiation consisting of 2 protons and 2 neutrons (a helium neutron)

Charge of +2e

Front 15

Air resistance

Back 15

The drag or resistive force experienced by objects moving through air

Front 16

Ammeter

Back 16

A device used to measure electric current

Must be placed in series and ideally has 0 resistance

Front 17

Amount of substance

Back 17

A measure of the amount of matter in moles

Front 18

Ampère

Back 18

The base SI unit of electric current, symbol A

Defined as the current flowing in 2 parallel wires 1m apart such that there is an attractive force of 2.0x10^-7 N/ metre length of wire between them

Front 19

Amplitude

Back 19

The maximum displacement from the equilibrium position

Hint 19

Waves

Front 20

Angle of incidence

Back 20

The angle between the direction of travel of an incident wave and the normal at a boundary between two media

Front 21

Angle of reflection

Back 21

The angle between the direction of travel of a reflected wave and the normal at a boundary between the two media

Front 22

Angular frequency

Back 22

A quantity used in oscillatory motion - equal to the product of frequency f and 2pi

Front 23

Angular velocity

Back 23

The rate of change of angle for an object moving in a circular path - symbol omega

Front 24

Anion

Back 24

A negatively charged ion, attracted to an anode

Front 25

Antiparallel vector

Back 25

Same line, opposite direction

Front 26

Antiparticle

Back 26

The antimatter counterpart of a particle

Opposite charge.

Same rest mass

Front 27

Antiphase

Back 27

Particles oscillating 180° out of phase. Completely out of step

Front 28

Aphelion

Back 28

The furthest point from the sun in an orbit

Front 29

Archimedes principle

Back 29

The upthrust on an object is equal to the weight of the fluid it displaces

Front 30

Arcminute

Back 30

A minute of arc. 1° = 60 arcminutes

Front 31

Arcsecond

Back 31

A second of arc; 1 minute of arc = 60 arcseconds

Front 32

Astronomical unit; AU

Back 32

The mean distance from the Earth to the Sun

150 million km

Front 33

Atomic mass unit (1u)

Back 33

1/12th the mass of a neutral Carbon 12 atom

Front 34

Binding energy per nucleon

Back 34

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 in the nucleus.

Front 35

Black body

Back 35

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

Front 36

Black hole

Back 36

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 need an escape velocity faster than the speed of light

Front 37

Boltzmann constant

Back 37

The molar gas constant R is divided by the Avogadro's constant

- relates mean KE of the atoms or molecules in a gas to the gas temperature

Hint 37

Symbol k

Front 38

Boyle's Law

Back 38

The pressure of an ideal gas is inversely proportional to its volume, provided that the mass and temperature of the gas do not vary

Front 39

Braking distance

Back 39

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

Front 40

Breaking strength

Back 40

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

Front 41

Brittle

Back 41

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

Front 42

Brownian motion

Back 42

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

Front 43

Capacitance

Back 43

The charge stored per unit potential difference across a capacitor

Hint 43

Unit F

Front 44

Capacitor

Back 44

A component that stores charge, consisting of two plates separated by an insulator

Hint 44

Dialectric

Front 45

Carbon dating

Back 45

A method for determining the age of organic material, by comparing the ratio of the carbon 14- carbon 12 nuclei of the dead material of interest compared to similar living material

Front 46

Cathode

Back 46

A - ve charged electrode

Front 47

Cation

Back 47

A positively charged ion

Hint 47

Attracted to the cathode

Front 48

Cell

Back 48

A device that transfers chemical energy into electrical energy

Front 49

Celsius scale

Back 49

A temperature scale with 100 degrees between the freezing and boiling point of pure water (at ATM 1.01 KPA)

Front 50

Centre of gravity

Back 50

An imaginary point at which the entire weight appears to act

Front 51

Centre of mass

Back 51

A point through which any externally applied force produces straight line motion but no rotation.

Front 52

Centripetal acceleration

Back 52

The acceleration of any object travelling in a circular path at constant speed

Hint 52

Always acts towards the centre of the circle

Front 53

Centripetal force

Back 53

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

Front 54

Chain reaction

Back 54

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

Front 55

Chandrasekhar limit

Back 55

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

1.44 solar masses

Front 56

Charge carrier

Back 56

A particle with charge that moves through a material to form an electric current

Hint 56

E.g. An electron in a metal wire

Front 57

Closed system

Back 57

An isolated system that has no interaction with its surroundings

Front 58

Cloud chamber

Back 58

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

Front 59

Atomic number

Back 59

The number of protons in a nucleus - symbol Z

Front 60

Attenuation

Back 60

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

Front 61

Average speed

Back 61

The rate of change in distance calculated over a complete journey

Front 62

Average velocity

Back 62

The change in displacement for a journey divided by the time taken

Front 63

Avocado constant

Back 63

6.02 x 10^23; the number of atoms in 0.012kg (12g) of carbon-12

Front 64

Background radiation

Back 64

The radiation emitted by the surroundings, which must be measured before radiation can be usefully be measured

Front 65

Baryon

Back 65

Any hadron made with a combination of three quarks

Front 66

Base unit

Back 66

One of seven units of the SI measurement system

Front 67

Battery

Back 67

A combination of cells that transfers chemical energy into electrical energy

Front 68

Beta decay

Back 68

A neutron in an unstable neutron decays into

A proton, an electron and an electron antineutrino

(Beta - decay)

A proton decays into neutron, a positron and an electron neutrino

(Beta + decay)

Front 69

Big Bang

Back 69

The theory that at a moment in the past all the matter in the Universe was contained in a singularity, the beginning of space and time, that expanded rapidly outwards

Front 70

Binding energy

Back 70

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