Definitions Flashcards
Effort
the force applied to a machine to make it move
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
elasticity
property of a solid that enables it to regain its shape after it has been deformed or distorted
elastic limit
point beyond which a wire is permanently stretched
electrical conductor
an object that can conduct electricity
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
electric field strength, E
at a point in the electric field, is the force per unit charge on a small positively charged object at a point in the field
electric potential, V
at a point in the electric field is the work done per unit charge on a small positively charged object to move it from infinity to that point in the field
electrolysis
process of electrical conduction in a solution or molten compound due to ions moving to the oppositely charged electrode
electrolyte
a solution or molten compound that conducts electricity
electromagnetic induction
the generation of an emf when the magnetic flux linkage through a coil changes or a conductor cuts across magnetic field lines
electromagnetic radiation
an electric and magnetic wavepacket or photon that can travel through free space
electromagnetic wave
an electric and magnetic wavepacket or photon that can travel through free space
electromotive force (emf)
the amount of electrical energy per unit charge produced inside a source of electrical energy
electron
a lepton with rest mass 9.11x10e-31 kg and electric charge -1.60x10e-19 C
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.
electron volt
amount of energy equal to 1.6x10e-19 J defined as the work done when an electron is moved through a pd of 1V
endoscope
optical fibre device used to see inside cavities
energy
the capacity to do work
energy levels
the energy of an electron in an electron shell of an atom or the allowed energies of a nucleus
equilibrium
state of an object when at rest or in uniform motion
equipotential
a line or surface in a field along which the electric or gravitational potential is constant
escape velocity
the minimum velocity an object must be given to escape from the planet when projected vertically from the surface
excitation
process in which an atom absorbs energy without becoming ionized as a result of an electron inside an atom moving from an inner shell to an outer shell
excited state
an atom which is not in its ground state (i.e., its lowest ground energy state)
explosion
when two objects fly apart and the two objects carry away at opposite and equal momentums
exponential change
exponential change happens when the change of a quantity is proportional to the quantity itself. For an exponential decrease of a quantity x, (dx/dt = -the decay constant multiplied by x). The solution to this equation is x = x0 multiplies by e to the power of (-the decay constant x t) where x0 is an initial value of x
Faraday’s 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 turns N, the induced emf = -NA(change in B/ change in t)
field line
the direction of a line of force indicates the direction of the 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
first harmonic
pattern of stationary waves on a string when it vibrates at its lowest possible frequency
fission
the splitting of a 92U nucleus or a 94Pu nucleus into two approximately equal fragments. Induced fission is fission caused by an incoming neutron colliding with a 92U nucleus or a 94Pu nucleus
fission neutrons
neutrons released when a nucleus undergoes fission and which may collide with nuclei to cause further fission
Fleming’s left hand rule
rule that relates the directions of force, magnetic field and current on a current carrying conductor in a magnetic field
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 if induced in it
fluorescence
glow of light from a substance exposed to ultraviolet radiation; the atoms de-excite in stages and emit visible photons in the process
Beta plus radiation
Positrons (B+) emmited by unstable proton-rich nuclei (ie nuclei with a neutron/proton ratio smaller than for stable nuclei). Positrons emitted in solids or liquids travel no further than about 2mm before they are annihilated.
Absolute scale
Temperature scale in kelvins (K) defined in terms of absolute zero, 0K, and the triple point of water, 273.16K, which is the temperature at which ice, water and water vapour are in thermal equilibrium.
Absolute zero
The lowest possible temperature, the temperature at which an object has minimum internal energy.
Absolute temperature T
…in kelvin = temperature in degrees C +273(.15)
Acceleration
Change of velocity per unit time.
Acceleration of free fall
Acceleration of an object acted on only by the force of gravity.
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.
Alpha decay
Change in an unstable nucleus when it emits an alpha particle which is a particle consisting of two protons and two neutrons.
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 in air of no more than a few centimetres and is more ionising than beta or gamma radiation.
Amplitude
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.
Angular displacement
The angle an object in circular motion turns through. If its time period is T and its frequency is f, its angular displacement in time t, in radians = 2pift = 2pi*t/T
Angular speed (omega)
The rate of change of angular displacement of an object in circular (or orbital or spinning) motion.
Angular frequency (omega)
For an object oscillating at frequency f in simple harmonic motion, its angular frequency = 2pif
Annihilation
When a particle and its antiparticle meet, they destroy each other and become radiation.
Antibaryon
A hadron consisting of 3 antiquarks
Antimatter
Antiparticles that each have the same rest mass and, if charged, have equal and opposite charge to the corresponding particle.
Antimuon
The antiparticle of the muon.
Antineutrino
The antiparticle of the neutrino.
Antinode
Fixed point in a stationary wave pattern where the amplitude is a maximum.
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.
Antiquark
Antiparticle of a quark.
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 12C6, equal to 1.661x10^-27 kg.
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.
Avogadro constant (Na)
The number of atoms in 12g of the carbon isotope 12C6. Na is used to define the mole. Its value is 6.02x10^23 mol^-1.
Back EMF
EMF induced in the spinning coil of an electric motor or in any coil in which the current is changing (e.g. the primary coil of a transformer). A back EMF acts against the change of applied pd.
Background radiation
Radiation due to naturally occurring radioactive substances in the environment (e.g. in the ground or in building materials or elsewhere). Background radiation is also caused by cosmic radiation.
Baryon
A hadron consisting of three quarks.
Base units
The units that define the SI system (e.g. the metre, the kilogram, the second, the ampere).
Beta decay
Change in a nucleus when a neutron changes into a proton and an electron and an antineutrino are emitted if the nucleus is neutron-rich or a proton changes into a neutron and a positron and a neutrino are emitted if the nucleus is proton-rich.
force
rate of change of momentum
mass x acceleration for fixed mass
forced vibrations
vibrations (oscillations) of a system subjected to an external periodic force.
free-body force diagram
a diagram of an object showing only the forces acting on the object.
free electrons
electrons in a conductor that move about freely inside the metal because they are not attached to a particular atom.
free vibrations
vibrations (oscillations) where there is no damping and no periodic force acting on the system, so the amplitude of the oscillations is constant.
frequency
of an oscillating object is the number of cycles of oscillations per second.
friction
force opposing the motion of a surface that moves or tries to move across another surface.
fundamental mode of vibration
pattern of stationary waves on a string when it vibrates at its lowest possible frequency.
fusion (nuclear)
the fusing together of light nuclei to form a heavier nucleus.
fusion (thermal)
the fusing together of metals by melting them together.
gamma radiation
electromagnetic radiation emitted by an unstable nucleus when it becomes more stable. See pair production.
geostationary satellite
a satellite that stays above the same point in the earth’s equator as it orbits the earth because it’s orbit is exactly 24 hours and it orbits in the same direction as the earth’s direction of rotation.
gold leaf electroscope
a device used to detect electric charge.
gravitational constant (G)
the constant of proportionality in Newton’s law of gravitation.
gravitational field
the region surrounding an object in which it exerts a gravitational force on any other object.
gravitational field strength (g)
the force per unit mass on a small mass placed in the field.
- g = F/m, where F is the gravitational force on a small mass m.
- at distance r from a point mass M, and at or beyond the surface of a sphere of mass M, g = gM/r^2 where r is the distance to the centre.
gravitational force
an attractive force that acts equally on any two objects due to their mass.
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. At distance r from the centre of a spherical object of mass M,
V = -GM/r
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 GPE of a mass m moved through height h near the earth’s surface. ∆Ep = mg∆h
grid system
the network of transformers and cables that is used to distribute electrical power from power stations to users.
ground state
the lowest energy state of an atom.
hadron
particles and antiparticles that can interact through the strong interaction.
half-life
the time taken for the mass of a radioactive isotope to decrease to half of 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.
Hall probe
a device used to measure magnetic flux density.
heat (Q)
energy transfer due to difference of temperature.
heat capacity
the energy needed to raise the temperature of an object by 1K
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 sperate pipes to turn to steam which is used to drive turbines.
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.
ideal gas
a gas under conditions such that it obeys Boyle’s law.
ideal gas equation
pV = nRT, where p is the gas pressure, V is the gas volume, n is the number of moles of gas, T is the absolute temperature and R is the molar gas constant.
impulse
of a different acting on an object, force x time for which the force acts.
induced emf
the generation of an emf when the magnetic flux linkage through a coil changes or a conductor cuts across magnetic field lines.
induced fission
fission caused by an incoming neutron colliding with a
235 235
92 U nucleus or a 94 Pu nucleus causing it to split into two approximately equal fragments.
inertia
resistance of an object to change its motion.
Integration
Mathematical process of finding the area under the curve from its mathematical equation
Intensity of radiation
At a surface is the radiation energy per second per unit area at normal incidence to the surface
Interference
Formation of points of cancellation and reinforcement where two coherent waves pass through each other
Internal energy
Of an object is the sum of the random distribution of the kinetic and potential energy of its molecules
Internal resistance
Resistance inside a source of electrical energy; the loss of pd per unit current in the source when current passes through it
Ion
A charged atom
Ionisation
Process of creating ions
Ionising radiation
Radiation that produces ions in the substance it passes through. It destroys cell membranes and damages vital molecules such as DNA directly or indirectly by creating ‘free radical’ ions which reacts with vital molecules
Isotopes
Of an element or atoms which have the same number of protons in its nucleus but different numbers of neutrons
Kaon
A meson that consists of a strange quark or anti-quark and another quark or anti-quark
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)
Kinetic energy
The energy of a moving object due to its motion
E=mv^2
Kinetic theory of a gas
1) Assumptions; A glass consists of identical point molecules which do not attract one another.The molecules are in continual random motion colliding elastically with each other and with the container
2) pV=1/3Nmc^2
p-pressure V-volume of container N - number of molecules m-mass of each molecule c^2- The mean square speed of the gas molecule
Laser
Device that produces a parallel coherent beam of monochromatic light
Latent heat of fusion
The energy needed to change the state of the solid to a liquid without change of temperature
Latent heat of vaporisation
The energy needed to change the state of a liquid to a vapour without change of temperature
Lenz’s law
When a current is induced by an electromagnetic induction the direction of the induced current is always such as to oppose the change that causes the current
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
Lepton number
Electron number is assigned to every lepton and antilepton, On the basis that the total lepton number for each branch of the lepton family is always conserved
Light dependent resistor (LDR)
Resistor which is designed to have a resistance that changes with the light intensity
Limit of proportionality
The limits beyond which when a wire or a spring is stretched its extension is no longer proportional to the force that stretches it
control rods
rods made of 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.
coolant
a fluid that is used to prevent a machine 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.
Coulomb’s law of force
for two points Q1 and Q2 at distance apart r, the force F between the two charges is given by the equation F = Q1Q2/4πɛ0r^2, where ɛ0 is the permittivity of free space.
drag force
the force of fluid resistance on an object moving through the fluid.
couple
pair of equal and opposite forces acting on a body but not along the same line.
critical angle
the angle of incidence of a light ray must exceed the critical angle for total internal reflection to occur.
critical mass
the minimum mass of the fissile isotope (e.g., the uranium isotope 235 92 U) 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.
critical temperature of a superconducting material
temperature at and below which its resistivity is zero.
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.
damped oscillations
oscillations that reduce in amplitude due to the presence of resistive forces such as friction and drag.
- For a lightly damped system, the amplitude of oscillations decreases gradually.
- For a heavily damped system displaced from equilibrium then released, the system slowly returns to equilibrium without oscillating.
- For a critically damped system, the system returns to equilibrium in the least possible time without oscillating.
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, λ, of a matter particle depends on its momentum, p, in accordance with de Broglie’s equation λ = h/p = h/mv, where h is the Planck constant.
decay constant λ
the probability of an individual nucleus decaying per second.
decay curve
an exponential decrease curve showing how the mass or activity of a radioactive isotope decreases with time.
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.
density of a substance
mass per unit volume of the substance.
dielectric
material that increases the capacity of a parallel-plate capacitor to store charge when placed between the plates of a capacitor. Polythene and waxed paper are examples of dielectrics.
dielectric constant
See relative permittivity.
differentiation
mathematical process of finding the gradient of a line from its equation.
diffraction
the spreading of waves when they pass through a gap or round 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.
diffraction grating
a plate with many closely ruled parallel slits on it.
dispersion
splitting of a beam of white light by a glass prism into colours.
displacement
distance in a given direction.
dissipative forces
forces that transfer energy which is wasted.
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 270k of X-radiation to have the same effect as a certain dose of the ionising radiation. The unit of dose equivalent is the sievert (Sv).
drag force
the force of fluid resistance on an object moving through the fluid.
ductile
stretches easily without breaking.
dynamo rule
See Fleming’s right-hand rule.
eddy currents
induced currents in the metal parts of ac machines.
efficiency
the ratio of useful energy transferred (or the useful work done) by a machine or device to the energy supplied to it.
scalar
physical quantity with magnitude only
semiconductor
substance in which the number of charge carriers increases when the temperature is raised
SI system
scientific system of units
simple electric motor
electric motor with an armature consisting of a single coil of insulated wire
simple harmonic motion
motion of an object where the acceleration towards equilibrium position is proportional to the displacement of the object from equilibrium and in the opposite direction
sinusoidal curve
any curve with the same shape as a sine wave (or cosine wave)
specific heat capacity c
of a substance is the energy needed to raise the temperature of 1kg of the substance by 1K without changing the state (Q = mcΔT)
specific charge
value of unit charge per unit mass for a charged particle
specific latent heat of fusion
of a substance is the energy needed to change the state of 1kg of solid to liquid without a change in temperature (Q = ml)
specific latent heat of vaporisation
of a substance is the energy needed to change the state of 1kg of liquid to vapour without a change in temperature (Q = ml)
spectrometer
instrument used to measure wavelegths of light very accurately
speed
change in distance per unit time
stationary waves
wave pattern with nodes and antinodes formed when two (or more) progressive waves
stiffness constant
force per unit extension needed to extend a spring or wire
stopping distance
sum of the thinking and breaking distances
strain
extension per unit length of a solid when deformed
strangeness number
number assigned to every particle and antiparticle on the basis that strangeness is conserved in strong interactions, but not always in a weak reaction or decay
stress
force per unit cross-sectional, perpendicular area in a solid
strong interaction
interaction between two hadrons
strong nuclear force
force that holds the nucleons together; attractive between 2 to 3 fm, repulsive below 0.5 fm
sublimation
change of state when a solid changes directly into vapour
superconductor
material that has zero electrical resistance
superposition
effect of two waves adding together when they meet
temperature
degree of hotness of an object defined in terms of fixed points e.g. the triple point of water
terminal speed
maximum speed reached by an object when the drag force on it is equal and opposite to the force causing the motion of the object
thermal energy
internal energy of an object due to temperature
thermal equilibrium
when no overall heat transfer occurs between two objects at the same temperature
thermal nuclear reactor
nuclear reactor which has a moderator in the core
thermistor
resistor which is designed to have a resistance that changes with temperature
thinking distance
distance travelled by a vehicle in the time it takes the driver to react
threshold frequency
minimum frequency of light that can cause the photoelectric emission for a given metal
linear
two quantities are said to have a linear relationship if the change of one quantity is proportional to the change of the other
line of force or a field line
indicates the direction of the force
load
the force to be overcome by a machine when it shifts or raises an object
logarithmic scale
a scale such that equal intervals correspond to a change by a constant factor
longitudinal waves
waves with a direction of vibration parallel to the direction of propagation of the waves
magnetic flux
= BA for a uniform magnetic field of flux density B that is perpendicular to an area A. Its unit is the weber (Wb)
magnetic flux density
the magnetic force per unit length per unit current on a current carrying conductor at right angles to the field lines. Its unit is the Tesla (T)
magnetic flux linkage
= NBA where N is the number of turns in the coil and BA is the magnetic flux. Its unit is the Weber (Wb)
magnetic force
F = BILsin(angle) F = BIL if perpendicular to field F = BQvsin(angle) F = BQv if perpendicular to field
mass
measure of the inertia or resistance to a change of motion of an object
mass defect
(of a nucleus) the difference between the mass of the separated nucleons and the nucleus
mass number
the number of protons and neutrons in a nucleus
matter waves
the wave-like behaviour of particles of matter
mean kinetic energy
for a molecule in a gas at absolute temperature T, its mean KE is 3kT/2, where k is the Boltzmann constant
melting point
the temperature at which a pure substance melts
meson
a hadron consisting of a quark and an antiquark
metastable state
an excited state of the nuclei of an isotope that lasts long enough after alpha or beta emission for the isotope to be separated from the parent isotope
modal dispersion
the lengthening of a light pulse as it travels along an optical fibre, due to rays that undergo less total internal reflection
moderator
substance in a thermal nuclear reactor that slows the fission neutrons down so they can go on to produce further nuclear fission
mole
one mole of a substance consisting of identical particles is the quantity of substance that contains 6.02x10^23 particles of the substance
molar gas constant
R, where pV=nRT
molarity
the number of moles in a certain quantity of a substance
molar mass
the mass of one mole of a substance
moment of a force about a point
force x perpendicular distance from the line of action of the force to the point (pivot)
momentum
mass x velocity, its unit is kgm/s
motive force
the force that drives a vehicle
Beta minus radiation. (B-)
Electrons Electrons emitted by and stable neutron rich nuclei i.e. nuclei with a neutron/proton ratio greater than for stable nuclei.Beta minus radiation is stopped by about 5 mm of aluminium, has a range in airOf up to a metre and is less ionising than alpha radiation and more ionising than gamma radiation
Beta plus radiation (B+)
Positrons omitted by unstable proton rich nuclei are you nuclei with a neutron/proton ratio smaller than the stable nuclei. Positrons omitted in solids or liquids travel no father and about 2 mm before they are eliminated.
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
Binding energy per nucleon
The average work done per nucleon to separate a nucleus into its constituent parts. Defining energy per nucleon per the nucleus = the binding energy of the nucleus/mass number A. The binding energy per nucleon is greatest for iron nuclei of mass Number about 56. The binding energy curve is a graph of binding energy per nucleon against mass number A.
Boiling point
The temperature at which a pure liquid at atmospheric pressure boils.
Boyles Law.
For a fixed mass of gas at constant temperature, it’s pressure X its volume is constant. The gas that obeys Boyles Law is said to be an “ideal gas “.
Boltzmann constant
The molar gas constant divided by the Avogadro number.
Braking distance
The distance travelled by a vehicle in the time taken to stop it.
Breaking stress
See ultimate tensile stress
Brittle
Snaps without stretching or bending when subject to stress.
Brownian motion
The random and unpredictable motion of a particle such as a smoke particle caused by money choose of the surrounding substance colliding at random with the particle. It’s discovery provided evidence for the existence of atoms.
Capacitance
The charge stored per unit pd of a capacitor. The unit of capacitance is the farad (F), Equal to 1 coulomb per volt. For a capacitor of capacitance C at pd V, the charge stored, Q = CV
Capacitor energy
Energy stored by the capacitor. See equations in book. Doesn’t let me write in Brainscape.
Capacitor discharge
See book
Celsius scale
Temperature in degrees Celsius or °C 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
Centre of mass
The centre of mass of the body is the point through which a single force on the body has no turning affect.
Centripetal acceleration
See book
Chain reaction
A series of reactions in which each reaction causes a further reaction. The nuclear reactor each fission event is due to a neutron colliding with a uranium 235 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 fission neutron on average from each fission event produces a further fission event.
Charge carriers
Charged particles that smooth a substance When a pd is applied across it
Charles’s law
For a fixed mass of an ideal gas at constant temperature, its volume is directly proportional to its absolute temperature. Kelvin.
Circuit rule for current (Kirchhoffs 1st Law)
- For two or more components in series, the total PD across all the components is equal to the sum of the PDs Across each component.
- The son of the EMFs round a complete loop in a circuit = the song of the PDs round the loop.
Circuit rules for PD (Kirchhoffs 2nd law)
- For two or more components in series, the total PD across all the components is equal to the sum of the PDs across each component.
- The sum of the emf’s round a complete loop in a circuit = The sum of the PD’s round the loop.
Coherent
Two sources of waves are coherent if they omit waves with the constant face difference.
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.
Conservation rules
Conservation of energy, charge, baryon number, and lepton numbers applies to all particle interactions. Conservation of strangeness applies to strong interactions only.
