Key Words Flashcards
(420 cards)
1
Q
Amplitude
A
The maximum displacement from equilibrium of an oscillating object. For a transverse wave, it is the distance from the middle to the peak of the wave
2
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Centre of Mass
A
The point through which a single force on the body has no turning effect
3
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Charge carriers
A
Charged particles that move through a substance when a p.d. Is applied across it
4
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Breaking distance
A
The distance travelled by a vehicle in the time taken to stop it
5
Q
Capacitance
A
The charge stored per unit pd of a capacitor. The unit of capacitance is Farad, equal to one coulomb per volt. For a capacitor of capacitance C at pd V, the charge stored, Q=CV
6
Q
Energy
A
The capacity to do work
7
Q
Electron Volt
A
Amount of energy equal to 1.6x10^-19 J defined as the work done when an electron is moved through a pd of 1 V
8
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Ductile
A
Stretches easily without breaking
9
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Displacement
A
Distance in a given direction
10
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Decay curve
A
An exponential decrease curve showing how the mass or activity of a radioactive isotope decreases with time
11
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Couple
A
A pair of equal and opposite forces acting on a body but not along the same line.
12
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Critical angle
A
The angle of incidence of a light must exceed must exceed the critical angle for Total Internal Refraction to occur
13
Q
Escape velocity
A
The minimum velocity an object must be given to escape from a planet when projected vertically from the surface
14
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Elastic limit
A
Point beyond which a wire is permanently stretched
15
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Effort
A
The force applied to a machine to make it move
16
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First harmonic
A
Pattern of stationary waves on a string when it vibrates at its lowest possible frequency
17
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Laser
A
Device that produces a parallel coherent beam of monochromatic light
18
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Ground state
A
The lowest energy state of an atom
19
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Hadron
A
Particles and antiparticles that can interact through the strong interaction
20
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Free electrons
A
Electrons in a conductor that move about freely inside the metal because they are not attached to a particular atom
21
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Friction
A
Force opposing the motion of a surface that tries to move, or moves across another surface
22
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Gold leaf electroscope
A
A device used to detect electric charge
23
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Impulse
A
Of a force acting on an object, force x time for which the force acts
24
Q
Inertia
A
Resistance of an object to change of its motion
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Kaon
A meson that consists of a strange quark or antiquark and another quark or antiquark
26
Ion
A charged ion ((different no. Of protons/electrons))
27
Lepton
Electrons, muons, neutrinos, and their antiparticles are classified as leptons because they cannot interact through the strong interaction. They interact through the weak interaction and, in the case of electrons and positrons, through the electromagnetic interaction.
28
Isotopes
Of an element are atoms which have the same number of protons in each nucleus but different numbers of neutrons
29
Load
The force to be overcome by a machine when it shifts or raises an object
30
Longitudinal waves
Waves with a direction of vibration parallel to the direction of propagation of the waves
31
Mass
Measure of the inertia or resistance to change of motion of an object
32
Melting point
The temperature at which a pure substance melts
33
Meson
A hadron consisting of a quark and an antiquark
34
Moment of a force about a point
Force x perpendicular distance from the line of action of the force to the point
35
Momentum
Mass x velocity. The unit of momentum is kgms^-1
36
Muon
A lepton which is negatively charged and has a greater rest mass than the electron
37
Natural frequency
The frequency of free oscillations of an oscillating system
38
Neutrino
Uncharged lepton with a very low rest mass compared with the electron
39
Node
Fixed point in a stationary wave pattern where the amplitude is zero
40
Nucleon
A neutron or proton inside a nucleus
41
Ohm's law
The pd across a metallic conductor is proportional to the current, as long as the physical conditions do not change
42
Optical fibre
A thin flexible transparent fibre used to carry light pulses from one end to the other
43
Pair production
When a gamma photon changes into a particle and an antiparticle
44
Pascal
Unit of pressure or stress equal to 1Nm^-2
45
Path difference
The difference in distances from two coherent sources to an interference fringe
46
Period of a wave
Time for one complete cycle of a wave to pass a point
47
Photon
Each photon is a wave packet of electromagnetic radiation. The energy of a photon E=hf, where f = frequency of the radiation and h is the Planck constant
48
Pion
A meson that consist of an up or down quark and an up or down antiquark.
49
Plane-polarised waves
Transverse waves that vibrate in one plane only
50
Plastic deformation
Deformation of a solid beyond its elastic limit
51
Scalar
A physical quantity with magnitude only
52
Refraction
Change of direction of a wave when it crosses a boundary where it's speed changes
53
Progressive waves
Waves which travel through a substance or through space if electromagnetic
54
Quark
Protons, neutrons and other hadrons consist of quarks. There are three main types of quark, the up quark, down quark and strange quark. (Three other quarks are the charmed quark, top quark and bottom quark.)
55
Radial field
A field in which the field lines are straight and converge or diverge as if from a single point.
56
Resistance
Potential difference divided by current
57
Resistivity
Resistance per unit length x area of cross section.
58
Resonant frequency
The frequency of an oscillating object in resonance
59
Satellite
A small object in orbit round a larger object
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Speed
Change of distance per unit time
61
Spectrometer
Instrument used to measure light wavelength very accurately
62
Specific charge
Charge / Mass value of a charged particle
63
Sinusoidal curves
Any curve with the same shape as a sine wave
64
Semiconductor
A substance in which the number of charge carriers increase when temperature is raised
65
Stationary waves
Wave pattern with nodes and antipodes formed when two or more progressive waves of the same frequency and amplitude pass through each other
66
Stiffness constant
The force per unit extension needed to extend a wire or a spring
67
Stopping distance
Thinking distance + braking distance
68
Strain
Extension per unit length of a solid when deformed
69
Strangeness number
A strangeness number is assigned to every particle and antiparticle on the basis that strangeness is always conserved in the strong interaction, but not necessarily conserved in a weak interaction or a decay involving a strange quark or antiquark
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Stress
Force per unit area of cross section in a solid perpendicular to the cross section
71
Strong interaction
Interaction between two hadrons
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Sublimation
The change of state when a solid changes to a vapour directly
73
Superconductor
A material that has zero electrical resistance
74
Superposition
The effect of two waves adding together when they meet
75
Thermistor
Resistor which is designed to have a resistance that changes with temperature
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Time period
Time taken for one complete cycle of oscillations
77
Total internal reflection
A light Ray travelling in a substance is totally internally refracted at a boundary with a substance of lower refractive index, if the angle of incidence is greater than a certain value known as the critical value
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Transverse waves
Waves with a direction of vibration perpendicular to the direction of propagation of the waves
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Continuous light spectrum
Continuous range of colours corresponding to a continuous range of wavelengths
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Line emission spectrum
Characteristic coloured vertical lines, each corresponding to a certain wavelength
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Line absorption spectrum
Dark vertical lines against a continuous range of colours, each line corresponding to a certain wavelength
82
Ultimate tensile stress
Tensile stress needed to break a solid material
83
Uniform circular motion
Motion of an object moving at constant speed along a circular path
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Useful energy
Energy transferred to where it is wanted when it is wanted
85
Vector
A physical quantity with magnitude and direction
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Velocity
Change of displacement per unit time
87
W Boson
Carrier of the weak nuclear force; W bosons have non-zero rest mass and may be positive or negative
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Wavefronts
Lines of constant phase
89
Wavelength
The least distance between two adjacent vibrating particles with the same displacement and velocity at the same time
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Weak interaction
Interaction between two leptons
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Weak nuclear force
Force responsible for beta decay
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Weight
The force of gravity acting on an object
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Work done
Energy transferred by means of a force, work=force x distance moved in the direction of the force. The work done by a force F when it's point of application moves through displacement s at angle Ø to the direction of the force is given by W=FscosØ
94
Work function of a metal
Minimum amount of energy needed by an electron to escape from a metal surface
95
X Rays
Electromagnetic radiation of wavelength less than about 1 nm. X-Rays are emitted from an X-ray tube as a result of fast-moving electrons from a heated filament as the cathode being stopped on impact with the metal anode. X-rays are ionising and they penetrate matter. Thick lead plates are needed to absorb a beam of xRays
96
Yield point
Point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain
97
Young's fringes
Parallel bright and dark fringes observed when light from a narrow slit passes through two closely spaced slits
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Young modulus
Tensile stress / strain. Assuming the limit of proportionality has not been exceeded. The unit of the Young Modulus is pascal Pa which is equal to 1Nm^-1
99
Acceleration of free fall
Acceleration of an object acted on only by the force of gravity
100
Alpha decay
Change in an unstable nucleus when it emits an alpha particle which is a particle consisting of two protons and two neutrons
101
Angular speed w
The rate of change of angular displacement of an object in circular, orbital or spinning motion
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Anti baryon
A hadron consisting of three antiquarks
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Anti muon
Antiparticle of the muon
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Atomic number Z
Of an atom of an element is the number of protons in the nucleus of the atom. It is also the order number of the element in the periodic table
105
Beta decay
Change in a nucleus when a neutron changes into a proton and a B- and an antineutrino are emitted if the nucleus is neutron rich. Or, a proton changes to a neutron and a B+ particle and a neutrino are emitted if the nucleus is proton rich
106
Brittle
Snaps without stretching or bending when subject to stress
107
Capacitor energy
Energy stored by the capacitor
| E=(QV)/2=(CV^2)/2=(Q^2)/2C
108
Centripetal force
The resultant force on an object that moves along a circular path. For an object of mass m moving at speed v along a circular path of radius r, F=(mv^2)/r towards the centre of the circle
109
Cycle
Interval for a vibrating particle (or a wave) from a certain displacement and velocity to the next time the particle (or wave) that has the same displacement and velocity
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Damped oscillations
Oscillations that reduce in amplitude due to the presence of resistive forces such as friction and drag
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Lightly damped system
Amplitude of oscillations decreases gradually
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Heavily damped system
For a heavily damped system displaced from equilibrium then released, the system slowly returns to equilibrium without oscillating
113
Critically damped system
The system returns to equilibrium in the least possible time without oscillating
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Forced vibrations
Oscillations of a system subjected to an external periodic force
115
Free body force diagram
A diagram of an object showing only the forces acting on the object
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Free vibrations
Oscillations where there is no damping and no periodic force acting on the system, so the amplitude of the oscillations is constant
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Frequency
Of an oscillating object is the number of cycles of oscillation per second
118
Gamma radiation
Electromagnetic radiation emitted by an unstable nucleus when it becomes more stable
119
Geostationary satellite
A satellite that stays above the same point on the Earths equator as it orbits the Earth because its orbit is in the same plane as the equator, it's period is exactly 24hr and it orbits in the same direction as the earths direction of rotation
120
Gravitational constant G
The constant of proportionality in Newtons law of gravitation
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Gravitational field
The region surrounding an object in which it exerts a gravitational force on any other object
122
Lepton number
A lepton number is assigned to every lepton and antilepton, on the basis that the total lepton number for each branch of the lepton is always conserved
123
Light dependent resistor
Resistor which is designed to have a resistance that changes with light intensity
124
Limit of proportionality
The limit beyond which, when a wire or a spring is stretched, it's extension is no longer proportional to the force that stretches it
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Linear
Two quantities are said to have a linear relationship if the change of one quantity is proportional to the change of the other
126
Line of force / field line
The direction of a line of force/ field line indicates the direction of a force. An electric field line is the path followed by a free positive test charge. The gravitational field lines of a single mass point towards that mass
127
Magnetic flux Ø
Ø=BA for a uniform magnetic field of flux density B that is perpendicular to an area A. The unit of magnetic flux is the weber (Wb)
128
Magnetic flux density B
The magnetic force per unit length per unit current on a current carrying conductor at right angles to the field lines. The unit of magnetic flux density is the tesla (T) . B is sometimes referred to as the magnetic field strength
129
Motor effect
The force on a current carrying conductor due to a magnetic field
130
potential gradient
at a point in a field is the change of potential per unit change of distance along the field line at that point. The potential gradient = - the field strength at any point
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power
rate of transfer of energy = energy transferred ÷ time taken
132
Principle of conservation of momentum
when two or more bodies interact, the total momentum is unchanged, provided no external forces act on the bodies
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projectile
a projected object in motion acted on only by the force of gravity
134
refractive index
Speed of light in free space ÷ Speed of light in the substance
135
rest energy
energy due to rest mass m(0), equal to m(0)c^2, where c is the speed of light in free space
136
Simple electric motor
An electric motor with an armature consisting of a single coil of insulated wire
137
Strong nuclear force
Force that holds the nucleons together. It has a range of about 2-3 fm and is attractive down to distances of about 0.5 fm. Below that distance it is a repulsive force.
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Alpha radiation
Particles that are each composed of two protons and two neutrons. An alpha particle is emitted by a heavy unstable nucleus which is then less unstable as a result. Alpha radiation is easily absorbed by paper, has a range of in air of a few cm and is more ionising then beta or gamma radiation
139
Angular displacement
The angle an object in circular motion turns through. If its time period is T and its frequency f, its angular displacement in time t, in radians = 2(pi)ft = (2(pi)t)÷T
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Annihilation
When a particle and its antiparticle meet, they destroy each other and become radiation
141
Antimatter
antiparticles that each have the same rest mass and, if charged, have equal and opposite charge to their corresponding particle.
142
Circuit rule for current (Kirchoff's 1st law)
1. The current passing through two or more components in series is the same through each component 2. At a junction, the total current in = the total current out
143
Circuit rule for pd (Kirchoffs second law)
1. For one or more components in series, the total pd across all the components is equal to the sum of the pd's across each component
2. The sum of the emf's round a complete loop in a circuit = the sum of the pd's round the loop
144
centripetal acceleration
1. For an object moving at speed v in uniform circular motion, its centripetal acceleration a= (v^2)/r towards the centre of the circle. 2. For a satallite in circular orbit, its centripetal acceleration (v^2)/r=g
145
Conservation rules
Conservation of energy, charge, baryon number, and lepton numbers apllies to all particle interactions. Conservation of strangeness applies to strong interactions only.
146
de Broglie wavelength
A particle of matter has a wave-like nature which means that it can behave as a wave. For example, electrons directed at a thin crystal are diffracted by the crystal. The de Broglie wavelength of a matter particle depends on momentum, p, equal to mv. wavelength = h/p where h is the Planck constant
147
De-excitation
Process in which an atom loses energy by photon emission, as a result of an electron inside an atom moving from an outer shell to an inner shell or in which an excited nucleus emits a gamma photon.
148
Density of a substance
Mass per unit volume of the substance
149
Dielectric
material that increases the capacity of a parallel-plate capacitor to store charge when placed between the plates of the capacitor. Polythene and waxed paper are examples of dielectrics.
150
Periodic Force
A force that varies regularly in magnitude with a definite time period
151
Permittivity of free space
The charge per unit area in coulombs per square meter on oppositely charged parallel plates in a vacuum when the electric field strength between the plates is 1 volt per metre
152
Photoelectric effect
Emission of electrons from a metal surface when the surface is illuminated by light of frequency greater than a minimum value known as the threshold frequency
153
Positive temperature coefficient
The resistance of a metal increases when it's temperature is increased
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Positron
A particle of antimatter that is the antiparticle of the electron
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Potential difference
Work done or energy transfer per unit charge between two points when charge moves from one point to the other
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Potential divider
Two or more resistors in series connected to a source of pd
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Potential energy
The energy of an object due to its position
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Force
Rate of change of momentum
| MxA for fixed mass
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Gravitational force
An attractive force that acts equally on any two objects due to their mass.
160
Hooke's law
The extension of a spring is proportional to the force needed to extend it up to a limit referred to as its limit of proportionality
161
Integration
Mathematical process of finding the area under a curve from its mathematical equation
162
Intensity of radiation
At a surface is the radiation energy per square unit area at normal incidence to the surface. The unit of intensity is Js^-1m^-2 or Wm^-2
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Interference
Formation of points of cancellation and reinforcement where two coherent waves pass through each other
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Internal resistance
Resistance inside a source of electrical energy; the loss of pd per unit current in the source when current passes through it.
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Ionisation
Process of creating ions
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Drag force
The force of fluid resistance on an object moving through the fluid
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Dispersion
Splitting of a beam of white light by a glass prism into colours
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Electromagnetic induction
The generation of an emf when the magnetic flux linkage through a coil changes or a conductor cuts across magnetic field lines
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Electromagnetic wave
An electric and magnetic wave packet or photon that can travel through free space
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Elasticity
Property of a solid that enables it to regain its shape after it has been deformed or distorted
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Electrical conductor
An object that can conduct electricity
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Electric potential V
At a point in an electric is the work done per unit charge on a small positively charged object to move it from infinity to that point in the field
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Equilibrium
State of an object when at rest or in uniform motion
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Excitation
Process in which an atom absorbs energy without becoming ionised as a result of an electron inside an atom moving from an inner shell to an outer shell.
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Explosion
When two objects fly apart, the two objects carry away equal and opposite momentum
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Electron
A lepton of rest mass 9.11x10^31 kg and electric charge -1.6x10^-19 C
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Electromotive force emf
The amount of electrical energy per unit charge produced inside a source of electrical energy
178
Diffraction grating
A plate with many closely ruled parallel slits on it
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Excited state
An atom which is not in its ground state
180
Flemings left hand rule
Rule that relates the directions of the force, magnetic field and current on a current-carrying conductor in a magnetic field.
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Fluorescence
Glow of light from a substance exposed to ultraviolet radiation; the atoms de-excite in stages and emit visible photons in the process
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Gravitational field strength g
The force per unit mass on a small mass placed in the field
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Gravitational potential V
At a point in a gravitational field is the work done per unit mass to move a small object from infinity to that point.
184
Kinetic energy
The energy of a moving object due to its motion.
185
Lenz's Law
When a current is induced by electromagnetic induction, the direction of the induced current is always such to oppose the change that causes the current
186
Magnetic flux linkage Nø
Through a coil of N turns, Nø=NBA where B= is the magnetic flux density perpendicular to area A. The unit of magnetic flux and of flux linkage is the Weber (Wb) equal to 1Tm^2 or 1Vs
187
Matter waves
The wave like behaviour of particles of matter
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Model dispersion
The lengthening of a light pulse as it travels along an optical fibre, due to rays that undergo less total internal reflection
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Motive force
The force that drives a vehicle
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Negative temperature coefficient
The resistance of a semiconductor decreases when its temperature is increased
191
Neutron
An uncharged particle that has rest mass of 1.674x10^-27 kg. Neutrons are in every atomic nucleus except that of hydrogen (1.1H)
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Neutrino types (or branches)
There are three types of neutrinos, the electron neutrino, the muon neutrino and the tau neutrino
193
Pressure
The force per unit area that a gas or a liquid or a solid at rest exerts normally (at right angles to) a surface. Pressure is measured in pascals (Pa), where 1Pa=1Nm^-2
194
Angular frequency
For an object oscillating at frequency f in simple harmonic motion, it's angular frequency =2(pi)f
195
Antiparticle
There is an antiparticle for every type of particle. A particle and its corresponding antiparticle have equal rest mass, and if charged, equal and opposite charge
196
Back emf
Emf induced in the spinning coil of an electric motor or in any coil in which the current is changing (eg the primary cool in a transformer). A back emf acts against the change of applied pd
197
Beta minus radiation
Electrons emitted by unstable neutron rich nuclei. Beta minus radiation is stopped by about 5mm of aluminium, has a range in air of up to a metre and is less ionising than alpha radiation and more ionising than gamma radiation
198
Beta plus radiation
Positrons emitted by a proton rich nuclei. Positrons emitted in solids or liquids travel no further than about 2mm before they are annihilated
199
Capacitor discharge
Through a fixed resistor of resistance R; time constant = RC; exponential decrease equation for current/charge/pd = x=x(0)e^(-t/RC)
200
Base units
The units that define the SI system
201
Conservation of momentum
For a system of interacting objects is the total momentum of the objects remains constant provided no external resultant force acts on the system
202
Coulomb's law of force
For two point charges q1 and q2 at distance apart r, the force F between the two charges is given by the equation F=(q1q2)/4(pi)ę0r^2 where ę0 is the permittivity of free space
203
Critical temperature of a superconducting material
Temperature at and below which its resistivity is zero
204
Differentiation
Mathematical process of finding the gradient of a line from its equation
205
Diffraction
The spreading of waves when they pass through a gap or around an obstacle. X-Ray diffraction is used to determine the structure of crystals, metals and long molecules. Electron diffraction is used to probe the structure of materials. High-energy electron scattering is used to determine the diameter of the nucleus
206
Dissipative forces
Forces that transfer energy which is wasted
207
Eddy currents
Induced currents in the metal parts of ac machines
208
Efficiency
The ratio of useful energy transferred (or useful work done) by a machine or device to the energy supplied to it.
209
Elastic collision
An elastic collision is one in which the total kinetic energy after the collision is equal to the total kinetic energy before the collision
210
Electrically insulating materials
An electrical insulator is a material that cannot conduct electricity; a thermal insulator is a material that is a poor conductor of heat
211
Electric field strength E
At a point in an electric field is the force per unit charge on a small positively charged object at that point in the field
212
Electron capture
A proton-rich nucleus captures an inner-shell electron to cause a proton in the nucleus to change into a neutron. An electron neutrino is emitted by the nucleus. An x-ray photon is subsequently emitted by the atom when the inner shell vacancy is filled.
213
Energy levels
The energy of an electron in an electron shell of an atom or the allowed energies of a nucleus
214
Equipotential
A line or surface in a field along which the electric or gravitational potential is constant
215
Exponential change
Exponential change happens when the change of a quantity is proportional to the quantity itself
216
Faradays law of electromagnetic induction
The induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit. For a changing magnetic field in a fixed coil of area A and N turns, the induced emf =-NA(changeB/changet)
217
Newtons law of gravitation
The gravitational force force F between two point masses m1 and m2 at distance r apart is given by F=Gm1m2/r^2
218
Newtons FIRST LAW
An object continues at rest or in uniform motion unless it is acted on by a resultant force.
219
Newtons SECOND LAW
The rate of change of momentum of an object is proportional to the resultant force on it
220
Newtons THIRD LAW
When two objects interact, they exert equal and opposite forces on one another
221
efficiency
the ratio of useful energy transfered (or the useful work done) by a machine or device to which energy is supplied
222
Gravitational Potential Energy
at a point in a gravitational field is the work done to move a small object from infinity to that point. The change of gravitational potential energy of a mass m moved through height h near the Earth's surface dEp=mgdh
223
Grid System
The network of transformers and cables that is used to distribute electrical power from power stations to users.
224
Inverse Swuare Law (Force)
Newtons Law of Gravitation and Coulombs Law of force between electric charges are inverse swuare laws because the force between two point objects is inversely proportional to the square of the distance between the two objects.
225
Nucleus
the relatively small part of an atom where all the atom's positive charge and most of its mass is concentrated
226
Nucleon Number A
The number of neutrons and protons in a nucleus; also referred to as mass number
227
Phase difference
In radians, for two objects oscillating with the same time period, Tp, the phase difference = 2(pi)dt/Tp where dt is the time between successive instants when the two objects are at maximum displacement in the same direction
228
Polarised
The positive charge and the negative charge of a polarised molecule are displaced in opposite directions
229
Principle of conservation of energy
In any change, the total amount of energy after the change is equal to the total amount of energy before the change
230
Principle of moments
For an object in equilibrium, the sum of the clockwise moments about any point = the sum of the anti-clockwise moments about that point
231
Proton
A particle that has equal and opposite charge to the electron and has a rest mass of 1.673x10^27 kg which is about 1836 times that of the electron. Protons are in every atomic nucleus. The proton is the only stable baryon.
232
Quark model (Or Standard Model)
A quark can join with an antiquark to form a meson or with two other quarks to form a baryon. An antiquark can join with two other antiquarks to form an antibaryon
233
Relative permittivity
Ratio of the charge stored by a parallel-plate capacitor with dielectric filling the space between its plates to the charge stored without the dielectric for the same pd.
234
Renewable energy
Energy from a source that is continually renewed. E.g hydroelectricity or solar
235
Resonance
The amplitude of vibration of an oscillating system subjected to a periodic force is largest when the periodic force has the same frequency as the resonant frequency of the system. For a lightly damped system, the frequency of the periodic force = natural frequency of the oscillating system. At resonance, the system vibrates such that its velocity is in phase with the periodic force.
236
Satellite motion
For a satellite moving at speed v in a circular orbit of radius r round a planet, it's centripetal acceleration = v^2/r . Substituting v=2(pi)r/T where T is its time period, and g= GM/r^2 where M is the mass of the planet, T^2=(4(pi)^2/GM)r^3 Keplars 3rd law
237
Simple harmonic motion
Motion of an object if its acceleration is proportional to the displacement of the object from equilibrium and is always directed towards the equilibrium position
238
Time period of a pendulum
T=2(pi)(l/g)^1/2
239
Time period of a spring
T=2(pi)(m/k)^1/2
240
Terminal speed
The maximum speed reached by an object when the drag force on its equal and opposite to the force causing the motion of the object.
241
Thinking distance
The distance travelled by a vehicle in the time it takes the driver to react.
242
Threshold frequency
Minimum frequency of light that can cause photoelectric emission
243
Time constant
The time taken for a quantity that decreases exponentially to decrease to 0.37 (1/e) of its initial value. For the discharge of a capacitor through a fixed resistor, the time constant = resistance x capacitance
244
Transformer
Converts the amplitude of an alternating pd to a different value. It consists of two insulated coils, the primary coil and the secondary coil, wound round a soft iron laminated coil
245
Step down transformer
A transformer in which the rms pd across the secondary coil is less than the rms pd supplied across the primary coil
246
Step up transformer
A transformer in which the rms pd across the secondary coil is greater than the rms pd applied to the primary coil
247
Transformer rule
The ratio of the secondary voltage to the primary voltage is equal to the ratio of the number of secondary turns to the number of primary coils
248
Transformer efficiency
For an ideal transformer the output power = input power. Transformer inefficiency is due to: resistance heating of the current in each coil; the heating effect of eddy currents in the core; and heating caused by repeated magnetisation and demagnetisation of the core
249
Uniform field
A region where the field strength is the same in magnitude and direction at every point in the field
250
Electric uniform field
The electric field between two oppositely charged parallel plates is uniform. The electric field strength E =V/d where V is the pd between the plates and d is the perpendicular distance between the plates
251
Uniform gravitational field
The gravitational field of the earth is uniform over a region which is small compared to the scale of the earth
252
Uniform magnetic field
The magnetic field inside a solenoid carrying a constant current is uniform along and near the axis
253
Wave particle duality of matter particles
Electrons directed at a thin crystal are diffracted by the crystal demonstrating wave like properties. A beam of electrons is deflected in a magnetic field showing their particle like behaviour
254
Wave particle duality of photons
Photons have a particle like nature as seen in the photoelectric effect. As well as a wave like nature shown in diffraction experiments
255
Absolute scale
Temperature scale in kelvins (k) defined in terms of absolute zero, 0k, and the triple point of water, 273.16 K, which is the temperature at which ice water and vapour are in thermal equilibrium.
256
Boiling point
The temperature at which a pure liquid at atmospheric pressure boils.
257
Absolute zero
The lowest possible temperature, the temperature at which an object has minimum internal energy
258
Boyle's law
For a fixed mass of gas at constant temperature, it's pressure x its volume is constant. A gas that obeys Boyle's law is said to be an ideal gas.
259
Absolute temperature
In kelvin = temperature in C +273(.15)
260
Celsius scale
Temperature, in degrees Celsius is defined as absolute temperature in kelvins -273.15. This definition means that the temperature of pure melting ice is 0’c and the temperature of steam at standard atmospheric pressure is 100'c
261
Charles' law
For a fixed mass of an ideal gas at constant pressure, it's volume is directly proportional to its absolute temperature
262
Fleming's right hand rule
Rule that relates the directions of the induced current, magnetic field and velocity of the conductor when the conductor cuts across magnetic field lines and an emf is induced in it.
263
Hall Probe
A device used to measure magnetic flux density
264
Heat Q
Energy transfer due to a difference of temperature
265
Heat capacity
The energy needed to raise the temperature of an object by 1k
266
Heat exchanger
A steel vessel containing pipes through which hot coolant in a sealed circuit is pumped, causing water passing through the steel vessel in separate pipes to turn into steam which is used to drive turbines.
267
Ideal gas
A gas under conditions such that it obeys Boyle's law
268
Ideal gas equation
pV=nRT, where p is the gas pressure, V is the gas volume, n is the number of miles of gas. T is the absolute temperature and R is the molar gas constant
269
Activity A
Of a radioactive isotope, the number of nuclei of the isotope that disintegrate per second. The unit of activity is the becquerel (Bq), equal to 1 disintegration per second
270
Atomic mass unit u
Correctly referred to as the unified atomic mass constant. 1/12th of the mass of an atom of the carbon isotope 12,6 C. Equal to 1.661x10^-27
271
Avogadro constant Na
The number of atoms in 12g of the carbon isotope 12,6C. Na is used to define the mole. It's value is 6.02x10^23 mol^-1
272
Background radiation
Radiation due to naturally occurring radioactive substances in the environment. It's also caused by background radiation
273
Specific heat capacity c.
Of a substance is the energy needed to raise the temperature of 1kg of the substance by 1K without change of state. To raise the temperature of mass m of a substance from T1 to T2, the energy needed Q=mc(T2-T1).
274
Temperature
The degree of hotness of an object. Defined in terms of 'fixed points' such as the triple point of water =273.16K
275
Thermal energy
The internal energy of an object due to temperature
276
Mass defect
Of a nucleus is the difference between the mass of the separated nucleons and the nucleus
277
Nuclide of an isotope a,zX
A nucleus composed of z protons and (a-z) neutrons, where z is the proton number and a is the mass number.
278
Nuclear fusion
The fusing together of light nuclei to form a heavier nucleus
279
Thermal fusion
The fusing together of metals by melting them together
280
Inverse square law of intensity
The intensity of gamma radiation from a point source varies with the inverse of the square of the distance from the source. The same rule applies to radiation from any point source that spreads out equally without being absorbed
281
Half Life T1/2
The time taken for the mass of a radioactive isotope to decrease to half the initial mass or for its activity to halve. This is the same as the time taken for the number of nuclei of the isotope to decrease to half the initial number
282
Binding energy of a nucleus
The work that must be done to separate the nucleus into its constituent neutrons and protons. Binding energy=mass defect x c^2. Binding energy in MeV = mass defect in u x 931.3
283
Boltzmann constant k
The molar gas constant divided by the Avogadro number, R/Na
284
Brownian motion
The random and unpredictable motion of a particle such as a smoke particle caused by molecules of the surrounding substance colliding at random with the particle. Its discovery provided evidence for the existence of atoms
285
Control rods
Rods made from a neutron absorbing substance such as cadmium or boron that are moved in or out of the core of a nuclear reactor to control the rate of fission events in the reactor
286
Coolant
A fluid that is used to prevent a machine or device from becoming dangerously hot. The coolant of a nuclear reactor is pumped through the core of the reactor to transfer thermal energy from the core to a heat exchanger
287
Count rate
The number of counters per unit time detected by a Geiger Müller tube. Count rates should always be corrected by measuring a value then subtracting the background count rate
288
Decay constant
The probability of an individual nucleus decaying per second
289
Electrolysis
Process of electrical conduction in a solution or molten compound due to ions moving to the oppositely charged electrode.
290
Internal energy
Of an object is the sum of the random distribution of the kinetic and potential energies of its molecules
291
Mean kinetic energy
For a molecule in a gas at absolute temperature T, it's mean kinetic energy=(3/2)kT where k is the Boltzmann constant
292
Reactor core
The fuel rods and the control rods together with the moderator substance are in a steel vessel through which the coolant (which is also the moderator in a 'pressurised water reactor') is pumped
293
Specific latent heat of fusion
Of a substance is the energy needed to change the state of unit mass of a solid to a liquid without change of temperature
294
Chain reaction
A series of reactions in which each reaction causes a further reaction. In a nuclear reactor, each fission event is due to a neutron colliding with a 235,92U nucleus which splits and releases two or three further neutrons that can go on to produce further fission. A steady chain reaction occurs when one one fission neutron on average from each fission event produces a further fission event.
295
Electrolyte
A solution or molten compound that conducts electricity
296
Fission neutrons
Neutrons released when a nucleus undergoes fission and which may collide with nuclei to cause further fission.
297
Binding energy per nucleon
The average work done per nucleon to separate a nucleus into its constituent parts. The binding energy per nucleon of a nucleus = binding energy of the nucleus / mass number A. The binding energy per nucleon is greatest for iron nuclei of mass number about 56.
298
Critical mass
The minimum mass of the fissile isotope in a nuclear reactor necessary to produce a chain reaction. If the mass of the fissile isotope in the reactor is less than the critical mass, a chain reaction does not occur because too many fission neutrons escape from the reactor or are absorbed without fission
299
Dose equivalent
A comparative measure of the effect of each type of ionising radiation, defined as the energy that would need to be absorbed per unit mass of matter from 250k of X-radiation to have the same effect as a certain does of the ionising radiation. The unit of dose equivalent is the sievert (sv)
300
Fission
The splitting of a 235,92U nucleus or a 235,94Pu nucleus into two approximately equal fragments. Induced fission is fission caused by an incoming neutron colliding with a 235,92U nucleus or a 235,94Pu nucleus
301
Mean kinetic energy of a molecule of an ideal gas
(3/2)kT where the Boltzmann constant k=R/Na
302
Total kinetic energy of n moles of an ideal gas
(3/2)nRT
303
What are the assumptions of the kinetic theory of gas
A gas consists of identical point molecules which do not attract one another. The molecules are in continual random motion colliding elastically with each other and the container.
304
What is the pressure of N molecules of a gas in a container volume V according to the kinetic theory of gas
pV=(1/3)Nm(Crms)^2 where m is the mass of each molecule and (Crms)^2 is the mean square speed of the gas molecules
305
The ideal gas law
pV=nRT
Assuming the mean kinetic energy of a gas molecule = (1/2)m(Crms)^2 = (3/2)kT
306
Latent heat of fusion
The energy needed to change the state of a solid to a liquid without change of temperature
307
Latent heat of vaporisation
The energy needed to change the state of a liquid to a vapour without change of temperature
308
HOOKES LAW
The extension of a spring is proportional to the force needed to extend it up to a limit referred to as its limit of proportionality
309
Name two features of a graph of Force against extension that confirm that the tested material is obeying Hooke's law (below the limit of proportionality)
Straight line
Through the origin
310
Consider a single slit diffraction pattern, describe how the pattern would change if light of a longer wavelength was used
The MAXIMA would be further apart
311
Consider a single slit diffraction pattern, state two ways the appearance of the fringes would change of the slit was made narrower.
The light would be less intense.
| There would be increased separation of the MAXIMA.
312
When can TIR occur
TIR can only occur when the ray of light travels from a higher refractive index to a lower refractive index
313
Specific latent heat of vaporisation
For a substance is the amount of energy required to change the state of a unit mass of a liquid to a vapour without change of temperature. To change the state of mass m of a substance without change of temperature the energy needed Q=ml where l is the specific latent heat of vaporisation of the substance.
314
Thermal equilibrium
When no overall heat transfer occurs between two objects at the same temperature
315
Thermal nuclear reactor
A nuclear reactor which has a moderator in the core
316
Root mean square speed Crms
The square root of the mean value of the square of the molecule speeds of the molecules of a gas
317
What did Rutherford's Alpha scattering experiment show
It demonstrated that every atom contains a positively charged nucleus which is much smaller than the atom and where all the positive charge and most of the mass is located
318
Pressure Law
For a fixed mass of an ideal gas at a constant volume, it's pressure is directly proportional to its absolute temperature
319
Molarity
The number of moles in a certain quantity of a substance. The unit of molarity is the mol.
320
What is the value, symbol, and unit for the molar gas constant
8.31, r, JK(^-1)mol(^-1)
321
Mole
One mole of a substance consisting of identical particles is the quantity of substance that contains Na particles of the substance.
322
Moderator
Substance in a thermal nuclear reactor that slows the fission neutrons down so they can can go on to produce further fission
323
Metastable state
An excited state of the nuclei of an isotope that last song enough after an alpha or beta emission for the isotope to be separated from the parent isotope
324
Ionising radiation
Radiation that produces ions in the substances it passes through. It destroys cell membranes and damages vital molecules such as DNA directly or indirectly by creating Free Radical ions which react with vital molecules
325
Kepler's Third Law
For any planet, the cube of its mean radius of orbit r is directly proportional to the square of its time period T.
326
State what is meant by equilibrium in the context of forces
Equilibrium is a state of a system in which there is no resultant force and no resultant torque
327
Explain what is meant by the emf of the battery
Work done by the battery per unit charge
328
State and explain one possible use for a satellite travelling in a circular polar orbit
Monitoring weather, as the whole earth may be scanned
329
Describe the energy changes that take place as the Bob of a simple pendulum makes one complete oscillation, starting at its maximum displacement
gpe > ke > gpe > ke > gpe
Energy is lost to surroundings in overcoming air resistance
330
State the relationship between the gravitational potential energy, Ep, and the gravitational potential V, for a mass m placed in a gravitational field
Ep=mV
331
The speed of some charged particles gradually increases as their energy is increased by a circular particle accelerator. State and explain how the magnetic field in the accelerator must change as the speed of the particles is increased.
The field strength must increase, so that the centripetal force on the particles increases and r remains constant
332
Protons can interact with electrons by gravity and two other fundamental interactions. Identify these interactions and name the exchange particle involved
Weak Nuclear force - W boson
| Electromagnetic force - Photon
333
State and explain one reason why the core of an optical fibre is made as narrow as possible
To reduce multi mode dispersion, which would cause light travelling at different angles to arrive at different times (known as pulse broadening). A smaller core reduces signal loss and stops the signal getting weaker
334
A laser is used for a two slit interference experiment. It is then replaced by another laser emitting a shorter wavelength. State and explain the effect on the maxima spacing on the screen
Maxima will be closer together, spacing is proportional to wavelength, as wavelength decreases spacing increases (D and s are constant). A smaller wavelength = a smaller path difference
335
State newtons law of gravitation
The force of attraction between two point masses is proportional to product of masses and inversely proportional to the square of the distance between them.
336
For a spinning coil in a magnetic field, explain why the magnitude of the emf is greatest when the plane is parallel to the field
Induced emf is proportional to rate of change of flux. Flux changes as the coil is rotated, for a coil starting perpendicular to the field, flux is greatest at 0' and 180'. The RATE OF CHANGE OF FLUX, is greatest at 90' and 270' as the coil cuts the field lines perpendicularly
337
What is the quark structure of a meson
A quark and an antiquark
338
Describe the process by which Mercury atoms become excited in a fluorescent tube.
Electrons flow through the tube.
And collide with orbiting electrons in the Mercury atoms.
Raising the electrons to a higher energy level.
339
What is the purpose of the coating on the inside surface of the glass in a fluorescent tube
Photons emitted from Mercury atoms are in the ultra violet spectrum, they are high energy photons.
These photons are absorbed by the coating,
And the powder emits photons in the visible spectrum
Incident photons have a variety of different wavelengths
340
A stationary wave is formed on a steel string when it is plucked at its centre. Explain why a stationary wave is formed.
Progressive waves travel from the centre and reflect. Two progressive waves now travel in opposite directions along the string. The waves have the same frequency and amplitude, hence superposition occurs and a stationary wave is formed
341
A narrow beam of monochromatic red light is shon at a double slit arrangement. Parallel red and dark fringes form. Describe how the appearance of the fringes would differ if white light had been used instead of red light.
The central fringe would be white. The side fringes continuous spectra. The dark fringes would be closer together as the average wavelength of red light is larger than the average wavelength of white light.
342
State, in words, how the force acting on a body is related to the change in momentum of the body
The force acting on the body is equal to its rate of change of momentum
343
Explain why optical fibres used for communication need to have cladding
- keeps signal secure
- maintains quality by reducing pulse broadening
- prevents scratching of the core
- keeps core away from adjacent fibres to prevent crossover of information
- provides tensile strength to the very thin and fragile core
344
what does the gradient represent on a charge/time graph
current
345
Why should a transformer circuit contain a fuse
The fuse prevents thr transformer from overheating
346
Why is the fused placed in the primary circuit of a transformer, rather than the secondary circuit
So that all of the transformer is disconnected from the supply when fuse fails. If the fuse was in the secondary circuit the primary circuit would remain live
347
Why is it difficult to obtain a reliable age of an ancient boat using carbon dating.
The boat may have been made with the wood some time after the tree was cut down.
The background radioactivity may be high compared to the measured count rates.
The count rate is so low that there is statistical variation in the recorded results.
Possible contamination.
Uncertainty of the ratio of Carbon-14 in carbon thousands of years ago
348
Pair production can occur when a photon interacts with matter. Explain the process of pair production
A photo interacts with an orbital electron, this occurs so that the momentum of the photon is conserved. The energy of the photon is used to create a particle.
349
Explain why pair production cannot take place if the frequency of the photon is below a certain value.
The energy of a photon depends on frequency. If frequency is below a certain value there is not enough energy to provide the mass of the particles.
350
An atom can become excited through the absorbtion of photons. Explain why only photons of certain frequencies cause excitation in a particular atom.
Electrons occupy discrete energy levels and need to absorb an exact amount of energy to move to a higher level. Photons must have a certain frequency to provide this energy as e=hf. All of the energy of the photon is absorbed by an electron, it is a 1 to 1 interaction.
351
Why is it better for a rechargeable battery to have a lower internal resistance
Internal resistance limits current, so a battery with lower internal resistance can provide a higher current. Less energy is wasted so the charging process is quicker.
352
Distinguish between the nodes and antinodes that can be seen when stationary waves are formed on a vibrating string
At nodes displacement is always zero. At anti nodes the displacements have maximum amplitude
353
Light from a star is passed through a diffraction grating. Explain how the appearance of the first order beam can be used to deduce one piece of information about the gases that make up the outer layers of the stars
Dark lines (Fraunhofer Lines) in the spectrum reveal the composition of the star's atmosphere.
354
State one similarity and one difference between an elastic collision and an in elastic collision
Similarity. Momentum is conserved in both cases
| Difference. In an elastic collision Kinetic Energy is conserved. In an inelastic collision it is not.
355
What is the unit of electric field strength
Vm^-1 or (NC^-1)
356
What do all hadrons eventually decay to?
Protons
357
Explain what is meant by coherent sources
Sources emitting waves of the same wavelength & frequency with Constanta phase difference
358
What is the quark structure of a neutron
udd
359
What is the quark structure of a proton
uud
360
What is an isotope
An atom of an element with the same proton number but a different number of neutrons
361
Explain with reference to the work function why, if the frequency of the radiation is below a certain value, electrons are not emitted
The work function is the minimum energy (=hf) required for an electron to be released. Below a certain frequency the energy of an incident photon will be less than the work function.
362
State what is meant by a non ohmic conductor
A non ohmic conductor does not have a constant resistance
363
State and explain why it is important for car batteries to have a very low internal resistance
If it has a larger internal resistance then a larger current is required to start the car. A higher internal resistance increases 'lost volts' and so power is wasted
364
What is the unit of magnetic flux linkage
Weber (wb) =Tm^2 or Vs
365
How is the induced emf of a rotating coil related to its speed of rotation. And how does this affect current in the coil
The emf is proportional to the speed of rotation. Therefor:
- At low speeds, the current is high because induced emf is low
- At high speeds, the current is low because the induced emf is high
366
When is strangeness number not necessarily conserved
In a weak interaction ( or a decay involving strange quarks/antiquarks)
367
F=BQv, state the condition under which this equation applies
Magnetic field must be at a right angle to velocity
368
F=BQv in this equation why does B represent
Flux density (Tesla)
369
State what happens to a neutron that is incident on the moderator.
The neutron is slowed down to thermal levels
370
What is 0'c in K
0'c = 273.15K
371
Explain why using an inclined plane rather than free fall would produce data which is valid when investigating the motion of a falling object.
The motion of the falling object is shower so it is easier to get an accurate measurement of time.
372
State the law of conservation of angular momentum
the total angular momentum of a system remains constant provided no external torque acts on the system
373
Give examples of transverse waves
Electromagnetic radiation, the surface of water, rope
374
State three differences between a transverse wave and a longitudinal wave
- in a transverse wave the oscillation is perpendicular to wave travel
- transverse waves can be polarised
- all longitudinal waves require a medium
375
State applications of a polarising filter and give reasons for its use.
Sunglasses - reduces glare
Camera - reduce glare / enhance image
Stress analysis - reveal areas of high or low stress
3D glasses - create 3d effect for viewing pleasure
376
Explain what is meant by the binding energy of a nucleus
The energy required to split a nucleus into its constituent nucleons
377
Name sources of background radiation
```
Radon in the atmosphere
Rocks
Cosmic rays
Nuclear fallout
Carbon-14
```
378
State and explain how the mass of a nucleus is different from the total mass of its separated nucleons
The separated nucleons have a greater mass because of the energy added to separate the nucleons
379
Explain why nuclei in a star have to be at a high temperature for fusion to take place
The higher the temperature the greater the kinetic energies of the light nuclei in the star, these nuclei need a large kinetic energy to overcome the repulsive electromagnetic force and get close enough to each other for the strong nuclear force to become attractive.
380
What type of beta decay occurs in the CNO cycle
Beta +
381
Describe the changes made inside a nuclear reactor to reduce its power output and explain the process involved
The control rods are inserted further into the nuclear core, they will absorb more neutrons so reduce the number of further fission reactions
382
Is gravitational potential a vector or scalar quantity
Scalar
383
State the quark structure of K-, K+, and K0
K- ūs
K+ uš
K0 dš
384
Which particles does the strong nuclear force effect
Hadrons only
385
What is the exchange particle of the SNF
Gluons and Pions
386
State what is meant by work function
Minimum amount of energy needed by an electron to escape from a metal surface
387
Suggest why two lamps can have different power ratings but have the same light intensity output
In lamps energy is wasted as heat. In some lamps (such as a filament lamp) more energy may be wasted
388
State what is meant by electromotive force
The amount of electrical energy per unit charge produced inside a source of electrical energy
389
What characteristics of a strange particle make it different from a particle that is not strange
It contains a strange quark
| It decays via weak interaction, where strangeness is not conserved
390
State what is meant by the ionisation energy of an atom
The energy required to completely remove an electron in its ground state from the atom.
391
Define the moment of a couple
One of the forces times the perpendicular distance between the lines of action
392
With reference to the NZ graph explain why fission fragments are unstable and explain what type of radiation they are likely to emit initially.
Fission fragments are likely to be above the line of stability so will have a larger N:Z ratio than more stable nuclei. As they are neutron rich they are likely to be B- emitters.
393
Define the Avogadro constant
The number of atoms in 12 grams of carbon 12
394
Transverse electromagnetic waves are used for TV signals. Explain why it is important to correctly align the aerial of the TV in order to receive the strongest signal
Transmitted radio waves are often polarised. Aerial rods must be aligned in the same plane of the wave
395
What is the unit of magnetic flux density
Tesla
396
Bullet A has a greater velocity when fired than bullet B. Explain why the horizontal distance travelled by bullet B will be less than bullet A.
The vertical motion of both bullets is independent of horizontal motion. So both bullets are in the air for the same amount of time. Distance travelled is proportional to horizontal speed so bullet A will travel further
397
State differences between a W boson and a photon
A w boson is charged and has rest mass. A photon is uncharged, massless and has infinite range.
398
What are similarities between Hadrons and Leptons
They both experiance the weak interaction and if charged the electromagnetic interaction. They all have rest mass
399
In terms of the photoelectric effext explain why the emitted electrons have a range of kinetic energies up to a maximum value.
The energy of an incident photon is fixed according to its frequency. The elctron requires energy to escape the surface of the metal, overcoming the work function. The maximum kinetic energy is the energy of the photon minus work function. Deeper electrons require more energy to get to the surface so have less KE when they are emitted.
400
State and explain the effect on the emitted electrons of decreasing the frequency of the light incident on the metal surface whilst keeping intensity constant.
Decreasing the energy of incident photons decreases the maximum kinetic energy of the electrons. in addition fewer deeper electrons will be able to escape
401
Does an LDR increase or decrease with light intensity?
Decrease
402
What is the phase difference between a particles velocity and a particles displacement in SHM
(3(pi))/4
403
What type of radiation produces the greatest number of ion pairs per mm in air
Alpha particles
404
What is the typical range in air for an alpha and beta particle
Alpha - 0.04m
| Beta - 0.4m
405
Explain what is meant by a chain reaction, naming the materials and particles involved
Uranium-235 captures a neutron and splits into two smaller fission fragments releasing 2/3 neutrons. At least one of these will cause a further fission event.
406
Explain why the shielding around a thermal reactor core becomes radioactive.
It is bombarded with neutrons. Some of these neutrons are absorbed by the nuclei in the shielding, converting them into unstable isotopes
407
What is the name of the point beyond which the behaviour of an extended spring changes irreversibly
Elastic limit
408
Explain how the use of a single slit in a double slit arrangement makes the light from the two slits sufficiently coherent for fringes to be observed
The single slit acts as a point source diffracting light to both slits. The path difference between the single slit and either of the double slits is the same
409
Explain why a microwave ovens contains a rotating turntable on which the food is placed during cooking.
A microwave works by setting up a stationary wave where energy transfer is a maximum at antinodes. The turntable ensures that this maximum energy is distributed evenly.
410
What properties would be seen on a stress strain graph of a brittle material
A straight line to breaking stress indicates little plastic behaviour. The line would have a steep gradient (high young modulus)
411
What is the percentage change in the diameter of the probe when it's resistance increases by 1.6%
-0.8%
R=>1/d^2
412
State what is meant by ionisation
The removal of electrons from an atom
413
State why an alpha emitting isotope used in a fire alarm poses little risk to the user
Only a small quantity is needed and alpha radiation can only travel a few cm's in air
414
What should be done to the cable on a crane for it to lift double the load at the same strain and same acceleration as the initial load.
To lift double the load at the same acceleration, double the force is needed. A material with double the young modulus of the first cable should be used so that double the force produces the same strain for the same diameter as the first cable. Or the diameter of the initial cable should be at least (root)2 times bigger
415
What are the types of EM radiation in order from longest wavelength to shortest
Radio, Microwave, Infrared, Visible, UV, X-ray, Gamma
416
Explain why the surface used in a change in momentum experiment is important
If the surface is soft it may increase the time taken for the collision to occur hence the force applied is less.
417
Explain what is meant by a potential divider
Two or more resisters in series connected to a pd
418
Explain why a railway engineer would not strain tracks so they are relaxed at maximum temperature
The tracks are strained so that they are relaxed at the average temperature of an area, this is so that they spend as much time under as little tensile/compressive strain as possible
419
Under what conditions does the frequency of a pendulum equation apply
When the oscillations are of small amplitude
420
What is meant by the internal resistance of a battery
The resistance of the materials in the battery.
