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1

absolute uncertainty

a quantity giving the extremes a measured value falls within

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2

absolute zero

the temperature at which all random motion of molecules stops

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3

absorption spectra

the set of wavelengths of photons absorbed by a substance

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4

acceleration of free fall

the acceleration due to the pull of the Earth on a body

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5

accurate

a measurement where the systematic error is small and so close to the "true" value

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6

activity

the rate of decay of a radioactive sample

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7

albedo

the ration of scattered to incident intensity of radiation

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8

alpha particle

the nucleus of helium-4

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9

alternating current (ac)

current in which electrons oscillate instead of moving with the same drift speed in the same direction

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10

Amonton's law or Gay-Lussac's law

the relation between pressure and temperature of a fixed quantity of an ideal gas when the volume is kept constant

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11

amplitude

the largest value of the displacement from equilibrium of an oscillation

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12

angular frequency or angular speed

the ratio of angle turned to time taken

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13

angular momentum

the product of mass, speed and orbit radius of a particle

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14

angular separation

the angle that the distance between two objects subtends at the observer's eye

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15

antinode

a point in a medium with a standing wave where the displacement is momentarily a maximum

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16

anti-particle

a particle with the same mass as its particle but with all other properties opposite, such as electric charge

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17

atomic (or proton) number

the number of protons in a nucleus

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18

atomic mass unit

a unit of mass equal to 1/12 the mass of a neutral atom of carbon-12

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19

average speed

the ratio of distance travelled to total time taken

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20

average velocity

the ratio of displacement to total time taken

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21

Avogadro constant

the number of particles in one mole

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22

baryon

a particle made up of three quarks

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23

baryon number

a conserved quantum number; it is assigned to each quark, and by extension to baryons

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24

beta minus decay

a decay producing an electron and an anti-neutrino

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25

beta plus decay

a decay producing a positron and a neutrino

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26

binding energy

the minimum energy that must be supplied to completely separate the nucleons in a nucleus or the energy released when a nucleus is assembled

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27

black body

a theoretical body that reflects none of the radiation incident on it and so absorbs all of it

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28

blue-shift

a decrease in the observed wavelength

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29

boiling

the change from the liquid to the vapour state at a specific constant temperature

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30

Boyle's law

the relation between pressure and volume of a fixed quantity of an ideal gas when temperature is kept constant

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31

capacitance

the charge that can be stored on a capacitor per unit voltage

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32

centripetal acceleration

the acceleration due to a changing direction of velocity

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33

centripetal force

a force pointing to the centre of a circular path

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34

chain reaction

a self-sustaining reaction

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35

charge carrier

charged particles that are able to move, creating an electric current

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36

Charles' law

the relation between volume and temperature of a fixed quantity of an ideal gas when the pressure is kept constant

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37

coefficient of dynamic friction

the ratio of the force of friction to the normal reaction force on a body while the body is sliding on a surface

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38

coefficient of static friction

the ratio of the maximum force of friction that can develop between two bodies to the normal reaction force on a body while the body is at rest

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39

coherent

sources whose phase difference is constant in time

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40

compression

a point in a medium through which a wave is travelling that has maximum density

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41

condensation

the change from the vapour to the liquid state

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42

conduction

the transfer of heat through electron and molecular collisions

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43

conservation of energy

the principle that energy cannot be destroyed or created but can only be changed from one form into another

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44

conservation of momentum

when the net force on a system is zero, the total momentum of the system is constant

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45

conserved

a quantity that states the same before and after an interaction

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46

constructive interference

the superposition of two identical waves that arrive at a point in phase

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47

control rod

a rod that regulates the the rate of energy release in a nuclear fission reactor by regulating the absorption of neutrons

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48

convection current

motion of a fluid as a result of differences in fluid density

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49

convection

the transfer of heat in fluids through differences in fluid density

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50

Coulomb's law

the electric force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation

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51

crest

a point on a wave of maximum displacement

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52

critical angle

the angle of incidence for which the angle of refraction is a right angle

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53

critical mass

the smallest mass of fissionable material that can sustain fission reactions

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54

decay constant

the probability per unit time for a nucleus to decay

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55

destructive interference

the superposition of two identical waves that arrive at a point 180 degrees out of phase

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56

diffraction

the spreading of a wave past an aperture or an obstacle

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57

diffraction grating

a series of very many and very narrow slits

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58

diode

a device that lets current through it only in one direction

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59

diode bridge rectifier

a circuit that achieved full-wave rectification

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60

dipole

a pair of two equal and opposite electric charges

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61

direct current (dc)

current in which electrons move in the same direction with the same average drift speed

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62

discrete

energy that can take a set of specific values as opposed to a continuous range of values

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63

dispersion

the dependence of refractive index on wavelength

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64

displacement

the change in position; for an oscillation, the distance between the position of a particle and its equilibrium position

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65

Doppler effect

the change in measured frequency when there is relative motion between source and observer

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66

drag force

a force of resistance to motion

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67

eddy currents

small induced currents in a conductor where the flux is changing that dissipate energy

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68

efficiency

the ratio of useful work or power to input work or power

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69

elastic potential energy

the energy stored in a spring when it is compressed or stretched

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70

electric field strength

the electric force per unit charge experienced by a small point positive charge

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71

electric potential

the work done per unit charge by and external agent in bringing a small point positive charge from infinity to a point

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72

electric potential energy

the work that needs to be done by and external agent in order to bring a set of charges from where they were separated by an infinite distance to their current position

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73

electric resistance

the ratio of the voltage across a device to the current through it

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74

electromagnetic

an interaction mediated by the exchange of photons

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75

electromagnetic waves

transverse waves moving at the speed of light in vacuum consisting of oscillating electric and magnetic fields at right angles to each other

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76

electroweak interaction

the interaction that is the unification of the electromagnetic and weak nuclear interactions

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77

elementary particles

particles that have no constituents

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78

emf

the work done per unit charge in moving charge across the terminals of a battery

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79

emission spectrum

the set of wavelengths of photons radiated by a substance

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80

emissivity

the ratio of the intensity radiated by a body to the intensity radiated by a black body of the same temperature

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81

energy density

the energy that can be obtained from a unit volume of fuel

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82

equation of state

the equation relating pressure, volume, temperature and number of moles of a gas

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83

equilibrium

the state when the net force on a system is zero

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84

equipotential surfaces

set of points that have the same potential

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85

escape velocity

the minimum speed at launch so that a particle can move to infinity and never return

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86

exchange particle

an elementary particle used as the intermediary of an interaction

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87

excited state

a state of energy higher than the ground state

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88

family lepton number

a quantum number assigned to each lepton in each family

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89

Faraday's law

the induced emf in a loop is the rate of change of magnetic flux linkage through the loop

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90

Feynman diagram

a pictorial representation of an interaction

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91

first harmonic

the mode of vibration of a standing wave of lowest frequency

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92

flux linkage

the magnetic flux in a loop times the number of turns in the loop

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93

force pair

two forces acting on different bodies that are equal and opposite according to Newton's third law

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94

fractional uncertainty

the ratio of the absolute uncertainty to the mean value of a quantity

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95

free-body diagram

a diagram showing a body in isolation with all forces acting on it drawn as arrows

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96

freezing

the change from the liquid to the solid state at a specific constant temperature

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97

frequency

the number of full oscillations or waves in unit time

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98

fuel rods

containers of nuclear fuels in a nuclear fission reactor

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99

full-wave recitification

the turning of ac current into dc current during both halves of the cycle

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100

gamma ray

a photon

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