AQA Physics Definitions Flashcards
1
Q
Specific charge
A
the charge in coulombs divided by the mass in kilograms or charge to mass ratio
2
Q
Isotope
A
Isotopes are nuclei with the same number of protons but a different number of neutrons
3
Q
Photo-electric effect
A
the emission of electrons from metal surfaces by incident light of an appropriate frequency
4
Q
Work function
A
the minimum energy required for an electron to escape from the surface of a metal
5
Q
Threshold frequency
A
the minimum frequency of a photon to produce photoelectrons
6
Q
Electron volt
A
the energy given to an electron when it passes through a potential difference of 1V
7
Q
Ionisation energy of an atom
A
the minimum energy required to remove an electron from an atom in its ground state
8
Q
Excitation energy
A
the energy required to move an electron from a lower energy level to a higher energy level
9
Q
Line spectra
A
the characteristic wavelengths of light produced by individual excited atoms
10
Q
Electric current
A
the number of coulombs of charge passing a point every second
11
Q
Potential difference
A
the work done per unit charge in moving charges from one point in a circuit to another
12
Q
Resistance
A
the ratio of potential difference across a component to the current through it
13
Q
Ohmic conductor or resistor
A
the ratio of potential difference to current remains constant
14
Q
Ohms law
A
the current through a component is proportional to the potential difference across it
15
Q
Critical temperature
A
the temperature at or below which the resistivity of a superconductor becomes zero
16
Q
Kirchoff’s first law
A
the sum of the currents into the junction is zero
17
Q
Kirchoff’s second law
A
in any closed loop the sum of the emf equals the sum of the potential difference
18
Q
EMF
A
the total energy supplied per coulomb to charges as they pass through the battery or cell (before losing energy to internal resistance)
19
Q
Internal resistance
A
the resistance inside a cell, battery, or power supply
20
Q
Useful volts
A
the potential difference across the terminals of the power supply (terminal p.d.)
21
Q
Lost volts
A
the potential difference across the internal resistance of the power supply
22
Q
Route mean square
A
the square root of the mean of all the square values
23
Q
Time base
A
the control on an oscilloscope which changes the time it takes for the beam to cross the screen horizontally
24
Q
Y-gain
A
the control on an oscilloscope that changes the sensitivity of the vertical voltage scale
25
Scalar
a physical quantity which has magnitude only
26
Vector
a physical quantity which has magnitude and direction
27
Equilibrium
a object is in equilibrium when the resultant force on it is zero and the resultant torque is zero
28
Couple
two equal an opposite forces acting on a body but not along the same line
29
Moment/torque
the moment/torque about a point is the force multiplied by the perpendicular distance from the point to the line of action of the force
30
Principle of moments
for an object in equilibrium the sum of the clockwise moments equals the sum of anticlockwise moments. This apples about any point which is on or outside the object
31
Centre of mass
the point at which the whole mass of the object appears to act, and the point where a single force acting has no turning effect
32
Displacement
the distance an object has moved in a particular direction
33
Speed
distance divided by the time taken
34
Velocity
the displacement of the object divided by the time taken
35
Acceleration
the change in velocity divided by the time taken to change
36
Parabolic path
the shape of the path of a particle moving with a component of motion at right angles to a constant resultant force
37
Newton's first law
an object remains at rest of moves with a constant velocity providing no resultant external force is applied
38
Newton's second law
for a constant mass the acceleration of an object is proportional to the resultant force applied to it
39
Newton's third law
if object A applies a force F on object B, object B applies a force of -F on object A
40
Work
work done equals force multiplied by the distance moved in the direction of the force
41
Power
power equals work done divided by time (rate of transfer of energy)
42
Principle of conservation of energy
energy cannot be created or destroyed; it can only be changed from one form to another
43
Hooke's law
the extension of a spring or material is proportional to the tensile force applied up to the limit of proportionality
44
Elastic limit
the point beyond which a material or spring stretched will not return to its original length
45
Tensile stress
tensile force divided by the cross-sectional area of the material
46
Tensile strain
the extension of a solid divided by its original length when deformed
47
Plastic behaviour
a material undergoing plastic behaviour will not return to its original shape after deforming forces are removed
48
Fracture
when a material breaks - materials are compared by their ultimate tensile stress; the tensile stress needed to break the material
49
Brittleness
a brittle material will not undergo plastic deformation before fracture
50
Young's modulus
tensile stress divided by tensile strain (assuming the limit of proportionality has not been exceeded)
51
Amplitude
the maximum displacement from the equilibrium position of an oscillating object
52
Frequency
the number of oscillations per second
53
Wavelength
the distance between two consecutive particles in a wave that are in phase
54
Wavespeed
the speed of energy transfer through the medium
55
Path difference
the extra distance one of the waves coming from two sources has to travel to reach a point
56
Electromagnetic wave
a transverse wave consisting of a changing magnetic field at right angles to a changing electric field
57
Polarised waves
electromagnetic waves with an electric field vector in one plane only
58
Unpolarised waves
electromagnetic waves with an electric field vector in many directions
59
Refractive index
the absolute refractive index of a substance is the speed of light in a vacuum divided by the speed of light in the substance
60
Critical angle
the angle of incidence on a boundary between two media when the angle of refraction is 90
61
Total internal reflection
TIR occurs when the angle of incidence is greater than the critical angle, the substance at the boundary has a lower refractive index, and all the light is reflected within the substance
62
Step index fibre
there is a sudden change in refractive index between the core and the cladding
63
Stationary wave
a stationary wave is formed by two waves of the same frequency and similar amplitude travelling in opposite directions
64
Node
a point on a stationary wave with zero amplitude
65
Antinode
a point on a stationary wave with maximum amplitude
66
Fundamental frequency
the lowest frequency of a wave which will produce a stationary wave
67
Coherence
coherent waves have the same frequency and a constant phase relationship/difference
68
Fringe spacing
the distance between two consecutive maxima or minima in an interference pattern
69
Impulse
force multiplied by the time for which the force acts on the body
70
Principle of conservation of momentum
momentum in a collision is always conserved provided no resultant external forces are acting
71
Elastic collision
kinetic energy is conserved
72
Inelastic collision
kinetic energy is not conserved
73
Explosive collision
kinetic energy is increased due to transfer of energy from the explosion
74
Centripetal force
the resultant force applied to an object to keep it moving in a circle, directed towards the centre of the circle and at right angles to the direction of motion of the object
75
Angular speed
the rate of change of angular displacement in radians for an object in circular motion
76
Simple harmonic motion
the condition for SHM is that the acceleration is proportional, and in the opposite direction, to the displacement from the equilibrium position. The period of oscillation is independent of the amplitude
77
Energy in SHM
the energy of the oscillator is proportional to the amplitude squared. For an undamped oscillator the total energy remains constant
78
Free vibrations
the oscillator vibrates at its natural frequency
79
Resonance
the frequency of oscillation of the driver equals the natural frequency, and so maximum energy transfer occurs
80
Phase relationship in resonance
the driver leads the driven by a phase angle of pi/2 radians (90 degrees) or a time of T/4 seconds
81
Forced vibrations
the oscillator vibrates at the frequency of the driver
82
Newton's law of gravitation
the gravitational force between two objects is proportional to the product of their masses, and the inverse square of the separation of their centres of mass. The constant of proportionality is the universal gravitational constant (G). The force is always attractive
83
Field
an area in space that explains why one object will apply a force on another object without touching
84
Gravitational field strength
the force per unit mass placed at that point in the field
85
Electric potential (at a point)
the work done per unit positive charge in bringing a small test charge from infinity to that point
86
Electric field strength
the force per unit charge on a small positively charged object placed at a point in the field
87
Gravitational potential (at a point)
the work done per unit mass in bringing a small test mass from infinity to that point in the field
88
Inverse square law
applies to the strength of radial fields; if the distance from the centre of the field is doubled the strength of the field is reduced by a factor of four
89
Circular path
the path taken by a particle when force of constant magnitude is applied at right angles to the motion of the particle
90
Capacitance
the charge stored per unit p.d. of a capacitor
91
Time constant
the resistance times the capacitance, measured in seconds
92
Magnetic flux density
this is a measure of the magnetic field strength, units Tesla
93
Tesla
1 Weber per metre squared
94
Magnetic flux
the component of the magnetic flux density at right angles to a surface multiplied by the area of the surface through which it passes (units Weber)
95
Magnetic flux linkage
the amount of magnetic flux that passes through a coil or complete loop of wire, multiplied by the number of turns of the wire
96
Fleming's left hand rule
this predicts the relationship between the direction of force (movement, thuMb), the current (seCond finger) and the field direction (First Finger)
97
Cyclotron
a device which uses an alternating electric field and a uniform magnetic field to accelerate charged particles
98
Faraday's law
the size of the induced EMF in a conductor is proportional to the rate of change of magnetic flux linkage
99
Lenz's law
the direction of induced current flows opposite to the change that produces it (conservation of energy)
100
Transformer equation
the ratio of the number of turns in the primary coil and secondary coil equals the ratio of primary and secondary voltages
101
Rutherford scattering
the deflection of alpha particles using thin gold film
102
Absorption
when the energy of the ionising radiation is completely used to ionise atoms in a material
103
Background radiation
the ionising radiation that is present without a radioactive source (from sun, rocks, medical uses, nuclear fallout from weapons)
104
Random nature of radioactive decay
radioactive decay follows the laws of probability - one cannot predict which nucleus will decay or when
105
Activity
the total number of particles emitted by a source per second (measured in Becquerel)
106
Becquerel
the number of counts per second
107
Half life
the time for half of the undecayed atoms to decay
108
Decay constant
the constant that relates the rate of decay of a radioactive material to the number of undecayed particles in the sample
109
Alpha particle
a helium nucleus emitted from a nucleus of an atom at about 1/10th the speed of light
110
Beta particle
an electron emitted from the nucleus of an atom 9/10th the speed of light
111
Electron capture
when a nucleus absorbs an electron from an atomic energy level close to the nucleus causing a proton to change to a neutron and an electron neutrino to be emitted, accompanied by the emission of a high energy photon when electrons drop down to fill the gap left by the absorbed electron
112
Nuclear excited states
when the nucleus is left with excess energy after the emission of a particle - the nucleus has quantised energy levels and a gamma ray of fixed energy is emitted from the nucleus
113
Radius of closest approach
the closest distance an alpha particle will get to a nucleus when fired directly towards it
114
Electron diffration
the diffraction of a high energy electron by the nucleus
115
Nuclear density
the density of nuclear matter
116
Mass difference
the difference between the mass of all the individual protons and neutrons and the mass when they are combined together in a nucleus
117
Binding energy
the energy released when the nucleus is formed from individual protons and neutrons
118
Atomic mass unit (u)
the mass of a particle or nucleus measured in 'u' compared to the mass of a carbon 12 atom having a mass of exactly 12 u
119
Binding energy per nucleon
the binding energy divided by the total number of protons and neutrons in a nucleus
120
Fission
the splitting of a large nucleus into smaller nuclei
121
Fusion
the joining together of smaller nuclei to form a larger nucleus
122
Induced fission
slow moving (thermal) neutrons are absorbed by a large nucleus making it unstable, which then decays releasing energy and producing smaller nuclei
123
Chain reaction
after induced fission occurs neutrons are released which will go on to produce further induced fission reaction
124
Critical mass
the mass of nuclear matter is critical when every induced fission causes at least one further fission (this depends upon the mass and shape of the matter)
125
Moderator
the material in a nuclear reactor that is used to slow the neutrons by collision (material usually water or carbon)
126
Coolant in a nuclear reactor
a fluid used to stop a machine or device becoming dangerously hot. It is pumped through the core of a nuclear reactor to transfer the thermal energy to the heat exchanger which is used to boil water to drive turbines
127
Control rods
these are made of a material that absorbs neutrons and changes the amount of neutron flux in the reactor hence changing the rate of fission (usually boron)
128
Specific heat capacity
the heat energy needed to raise 1kg of the material by 1 kelvin without change of state
129
Specific latent heat
the energy needed to change the phase of 1kg of a material
130
Specific latent heat of vaporisation
the energy needed to change the state of 1kg of a material from liquid to gas without change of temperature
131
Ideal gas
a gas that obeys Boyle's law (pV=k) or the ideal gas equation (pV=nRT)
132
Avagadro's constant
the number of particles in one mole of carbon-12 (in exactly 12g of carbon-12)
133
Molar mass
the mass of one mole of a substance
134
Molecular mass
the mass of one particle in a gas
135
Assumptions in the kinetic theory of gases
- the particles apply a force on the walls of the container by collision
- collisions of particles with the walls and eachother are elastic
- no bonds between particles
- gas particles move with random motion
- there are a large number of particles
- the volume of the particles is negligible compared to the volume of the container
- contact time of collisions with walls is negligible compared with time between collisions with walls
136
Frequency of a progressive wave
number of complete cycles/wavelengths passing
| a point per second
137
Why is gravitational potential negative
Gravitational potential is defined as zero at infinity, and as the force is attractive, work must be done to reach infinity, hence it is always negative
138
Black hole
An object with an escape velocity greater than the speed of light
139
Escape velocity
The velocity at which an objects kinetic energy is equal to minus its gravitational potential energy, or the minimum speed that will allow an object to escape the gravitational field
140
Modal dispersion
Light rays enter fibre at different angles and so some travel longer distances. Use a single-mode fibre to prevent this
141
Material dispersion
Different wavelengths of light travel at different speeds in the fibre. Use monochromatic light to prevent this
142
Yield point
the stress at which a large amount of plastic deformation takes place with a constant load
143
Internal energy
Internal energy is the sum of the randomly distributed kinetic energies and potential energies of the particles in a body
