A2 Physics Terms Flashcards
Absolute scale (Thermal)
Temperature scale in Kelvins 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 water vapour are in thermal equilibrium.
Absolute zero
- The lowest possible temperature;
2. The temperature at which an object has minimum internal energy.
Absolute temperature T
in kelvin = temperature in degrees Celsius + 273(.15)
activity A
of a radioactive isotope, is the number of nuclei of the isotope that disintegrate per second.
Unit: Becquerel (Bq) - 1 disintegration per second.
Alpha decay
change in an unstable nucleus when it emits an alpha particle, which is a particle consisting of 2 protons and 2 neutrons (a helium nucleus).
Alpha radiation (Composition, Emission circumstances, Absorption, Range, Comparison of Ionisation ability)
- Particles composed of 2 p + 2n
- Alpha particle is emitted by a heavy, unstable nucleus, which is then less unstable as a result.
- Alpha radiation easily absorbed by paper,
- Range of no more than a few centimetres.
- More ionising than Beta or Gamma radiation.
Amplitude
the maximum displacement from equilibrium of an oscillating object
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 is = 2 PI f t = 2 PI t/T
Angular speed, w
the rate of change of angular displacement of an object in circular (or orbital or spinning) motion.
Angular frequency, w
for an object oscillating at frequency f in simple harmonic motion its angular frequency = 2 PI f
Atomic mass unit u
correctly referred to as the unified atomic mass contestant,
- Equals 1/12 th of the mass of at atom of the carbon isotope 12,6 C = 1.661 x 10^-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, N(a)
The number of atoms in 12g of th carbon isotope 12,6 C.
- N(a) is used to define the mole
- Its value is 6.02 x 10^23 1/mol
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 coli in a transformer
A back emf acts against the 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 in the environment).
Background radiation is also caused by cosmic rays.
Beta decay
- Change in nucleus when a neutron changes in a proton and a beta minus particle and an antineutrino are emitted if the nucleus is neutron-rich.
- OR a proton changes to a neutron, and a beta plus particle and a neutrino are emitted if the nucleus is proton rich.
Beta minus radiation
electrons (beta particles) emitted by unstable neutron rich nuclei (e.g. nuclei with a neutron/proton ratio greater than for stable nuclei).
- B minus radiation is easily absorbed by paper,
- Has a range in air of no more than a few centimetres,
- Is less ionising than alpha radiation, and but more ionising than gamma radiation.
Beta plus radiation
Positrons emitted by unstable proton rich nuclei (i.e. nuclei with a neutron/proton ratio smaller than for stable nuclei).
Positrons emitted in solids or liquids travel no further than about 2 mm before they are annihilated.
Binding energy of a nucleus
The work that must be done to separate a 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.
- The binding energy per nucleon of a nucleus = binding energy of a 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.
Boyle’s law
For a fixed mass of gas at constant temperature, its pressure x volume is constant.
A gas that obeys Boyle’s law is said to be an ideal gas.
BL: pV = k, constant m, T
Boltzmann Constant, k
the molar gas constant divided by the Avogadro number = R/N(a).
See KE of molecules of an ideal gas
Brownian motion
The random and unpredictable motion of a particle such as smoke, caused by molecules of the surrounding substance colliding at random with the particle.
Capacitance
The charge stored per unit pd of a capacitor.
- Unit: Farad (F) = 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,
E = 1/2 QV
= 1/2 CV^2
= 1/2 Q^2/C
Capacitor discharge
Capacitor discharge through a fixed resistor of resistance R, time constant RC, exponent decrease equation for current / charge / pd (:= x), is
x = (x0) e^( - t / RC )
Celsius scale
temperature, in degrees Celsius, is defined as absolute temperature (in Kelvins) minus 273.15.
This definition means that the temperature of pure melting ice (ice point) is 0 degrees C, and the temperature of steam at standard atmospheric pressure (steam point) is 100 degrees C.
Centripetal acceleration
- For an object moving at linear speed v (or angular speed w) in UCM its centripetal acceleration a = v^2/r = w^2*r directed towards the centre of the circle of rotation.
- For a satellite in a circular orbit, its centripetal acceleration v^2 / r = g
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, the centripetal force
Fc = mv^2/r = mrw^2
towards the centre of the circle
Chain reactions
- 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, 92 U nucleus which splits and releases 2 or 3 further neutrons that can go on to produce further fission.
- A steady chain reaction occurs when one fission neutron on average produces a further fission event.
Charles’ Law
For an ideal gas at constant pressure, its volume is directly proportional to its absolute temperature.
- For constant P, m, : V = kT
Principle of COLM
For a system of interacting objects, the total momentum of the objects remains constant provided no external resultant force acts on the system.
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 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.
Coulomb’s law of force
for two point charges Q1 and Q2, at a distance apart r,
the force F between the two charges is given by the equation F = Q1Q2 / (4 PI e0) r^2 where e0 is the permittivity of free space.
Count rate
the number of counts per unit time detected by a Geiger Mueller tube.
- Count rates should always be corrected by measuring and subtracting the background count rate (i.e. the count rate with no radioactive source present).
Critical mass
The minimum mass of the fissile isotope (e.g. 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.
Damped oscillations
oscillations that reduce in AMPLITUDE due to the presence of resistive forces, such as friction and drag.
–> Light/heavy/ critical damping
Light damping
For a lightly damped system, the amplitude of oscillations decreases gradually.
Critical damping
For a critically damped system, the system returns to equilibrium in the least possible time without oscillating.
Heavy damping
For a heavily damped system displaced from equilibrium then released, the system slowly returns to equilibrium without oscillating.
de Broglie wavelength
- Matter particles have a wave-like nature which mean that they can behave like waves e.g. electron diffraction
- dBW depends on momentum p,
lambda = h/p = h / (mv)
decay constant, lambda
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.
Displacement
distance in a given direction
Differentiation
…
Diffraction
The spreading of waves when they pass through a gap or round an obstacle.
examples:
1. Xray diffraction – determination of the structure of crystals, metals and long molecules.
2. Electron diffraction – electron microscopy.
3. High energy electron scattering is used to determine the diameter of a nucleus.
Dynamo rule
= Fleming’s RIGHT HAND RULE
Eddy currents
Unwanted induced currents in the metal parts of AC machines.
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.
Electrical conductor
An object that can conduct electricity
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.
Electric potential, V
Electric potential, V at a point in an 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.
Electromagnetic induction
The generation of an emf when the magnetic flux linkage through a coil changes, or a conductor cuts across magnetic field lines.
Electron
A lepton of rest mass … and charge….
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.
Equilibrium
A state of an object when at rest or in uniform motion
Equipotential
A line or surface in a field along which the gravitational / electric POTENTIAL is constant.
Excited state
An atom which is not in its ground state, i.e. its lowest energy state.
Explosion
when two objects fly apart, the two objects carry away equal and opposite momentum.
Exponential change
….
Faraday’s law of EM 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 *(dB/dt)
Field line
= Line of force
Fission
- The splitting of a (235, 92) U / (235, 94)Pu nucleus, into 2 approximately equal fragments.
- Induced fission is fission caused by an incoming neutron colliding with a (235, 92) U nucleus or a (235, 94) Pu nucleus.
Fission neutrons
Neutrons released when a nucleus undergoes fission and which may collide with nuclei to cause further fission.
Flemings LEFT HAND RULE
Flemings LHR :
- Relates the directions of the FORCE (F), magnetic field (B) and current (I) on a current carrying conductor in a magnetic field.
Remember FBI and LHR
Fleming’s RIGHT HAND RULE/ Dynamo Rule
FRHR : Rule that relates directions of the INDUCED CURRENT, MAGNETIC FIELD, VELOCITY of the Conductor, when the conductor cuts across magnetic field lines and an emf is induced in it.
Force
:= the rate of change of momentum = change in momentum / time taken = mass x accelerator for a fixed mass.
Free electrons
electrons in a conductor that move about freely inside the metal because they are not attached to a particular atom.
Free oscillations
Oscillations where there is no damping and no periodic force acting on the system and so the amplitude of the oscillations is constant.
Forced oscillations
oscillations of a system that is subjected to an external periodic force.
Frequency
… of an oscillating object is the number of cycles of oscillation per second.
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
EM Radiation emitted by an unstable nucleus when it becomes more stable.
Geostationary satellite
A satellite that stays above the same point on the Earth’s equator as it orbits the Earth because its orbit is in the same plane as the equator, its period is exactly 24 h 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
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, g = GM/r^2 (radial field)
- At, or beyond a sphere of mass M, g = GM/r^2 where r is the distance to the centre.
- At the surface of a sphere of mass M and radius R, g(surface) = GM/R^2
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 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 gravitational potential energy of a mass m moved through height h near the Earth’s surface, dEp = mg dh.
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
Half life T(1/2)
- 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.
Hall probe
A device used to measure magnetic flux density
heat Q
energy transfer due to a difference of temperature
Heat capacity
the energy needed to change the temperature of an object by 1 K
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 to steam which is used to drive turbines.
Ideal gas
A gas under conditions such that it obey’s Boyle’s law
Ideal gas equation
pV = nRT, where p = gas pressure V = gas's volume n = number of moles of gas T = absolute temperature R = molar gas constant
Impulse
Impulse of a force acting on an object = force x time (for which the force acts).
Induced emf
see EM induction ????????
Induced fission
See fission??????
Electrical insulator
A material that cannot conduct electricity
Thermal insulator
A material that is a poor conductor of heat
Integration
….
Intensity of radiation
Intensity of radiation at a surface is the radiation energy per second per unit area at normal incidence to the surface.
Unit of intensity = J / s / m^2 = W / m^2
Internal energy, U
The sum of the random distribution of the kinetic and potential energies of an object’s molecules.
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.
Isotopes
Isotopes of an element are atoms which have the same number of protons in each nucleus but different numbers of neutrons.
Inverse square laws
x proportional to 1/y^2. Force 1. NLG : 2. CFL Intensity 1. Radiation intensity from a point source varies with the inverse f square of the distance from the source. The same rule applies to radiation from any point source that spreads out equally in all directions and is not absorbed.
Kepler’s Third Law
….
Kinetic energy
…
Kinetic energy of the molecules of an ideal gas.
- Mean kinetic energy of a molecule of an ideal gas = 3/2 kT (k = Boltzmann constant).
- Total KE of n moles of ideal gas = 3/2 nRT
Kinetic theory of a gas
- Assumptions : a gas consists of identical point molecules, which don’t attract one another, molecules in continual random motion, colliding elastically with each other and with the container.
- pV = 1/3 Nmc(rms)^2
- KE = 3/2 kT, together with (2) shows that the assumptions of kinetic theory produce ideal gas behaviour (ie. that pV = nRT)
Kinetic theory of gases equation
pV = 1/3 Nmc(rms)^2
Latent heat of fusion
the energy needed to change the state of a solid to a liquid without change of temperature
Latent heat of vaporisation
The energy needed to change the state of liquid to a vapour without change of temperature.
Lenz’s Law
When a current is induced by EM induction, the direction of the induced current is always such as to oppose the change that causes the current.
Line of force/field line
A line followed b a small mass in a gravitational field (or a small positively charged object in an electric field , or a free north pole in a magnetic field) acted on by no other forces than the force due to the field.
Logarithms/ Logarithmic scale / Log graphs
….
Magnetic flux : PHI
PHI = BA for a uniform magnetic field of flux density B that is perpendicular to an area A.
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.
Magnetic flux linkage, N*phi
through a coil of N turns = N*Phi = NBA where B is magnetic flux density perpendicular to area A. The unit of magnetic flux and of flux linkage is the Weber (Wb), equal to 1 T m^2 or 1 V s.
*Magnetic force on a current carrying wire in a uniform magnetic field at angle Theta to field lines
F = B I L sin theta
- Direction – FLHR
*Magnetic force on a moving particle of charge Q moving through a uniform magnetic field at speed v at direction at angle theta to the field
F = BQv sin theta
- Direction : F LHR
- Current is conventional current (i.e. equivalent direction of positive charge flow)
*Radius of the orbit of a charge moving in a direction at right angles to the lines of a magnetic field
BQv = mv^2/r
Mass defect
mass defect of a nucleus is the difference between the mass of the separated nucleons (i.e. protons and neutrons from which the nucleus is composed) and the nucleus.
Mean kinetic energy
For a molecule in a gas at absolute temperature T, its mean kinetic energy 3/2 kT
Melting point
The temperature at which a pure substance melts
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 e.g. 99-Tc
Moderator
Substance in a thermal nuclear reactor that slows the fission neutrons down so that they can go on to produce further fission.
Mole
One mole of substance consisting of identical particles is the quantity of substance that contains N(A) particles of the substance.
Molar gas constant
R - see ideal gas equation
Molarity
The number of moles in a certain quantity of a substance.
Unit: mol
Molar mass
The mass of one mole of a substance
Momentum
= mass x velocity
Unit : kg m/s
Motor effect
the force on a current carrying conductor due to a magnetic field.
Natural frequency
the frequency of free oscillations of an oscillating system
Neutron
….
Newton’s law of gravitation
the gravitational force F between two point masses m1 and m2 is given by F = G m1m2 / r^2
N1L
An object continues at rest or in uniform motion unless it is acted on by a resultant force
N2L
- The rate of change of momentum of an object is proportional to the resultant force on it.
- F = dP/dt
- For constant mass dP = m dV so F = m dv/dt = ma
Nucleon
A neutron or a proton in the nucleus
Nucleus
The relatively small part of an atom where all the atom’s positive charge and most of its mass is concentrated .
Nuclide of an isotope (A, Z) X
a nucleus composed of Z protons and (A - Z) neutrons where Z is the proton number (and also the atomic number of element Z) and A is the mass number (i.e. the number of protons and neutrons in a nucleus).
Pair production
When a gamma photon changes into a particle and an antiparticle.
Periodic force
A force that varies regularly in magnitude with a definite time period
Permittivity of free space
e0:
- The charge per unit area in coulombs per square metre on oppositely charged parallel later in a vacuum when the electric field strength between the plates is 1 volt per metre.
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 displacements in the same direction.
Photon
Electromagnetic radiation consists of photons.
Each photon is a wave packet of EM radiation,
The energy of a photon, E = hf, where f is the frequent of the radiation and h is Planck’s constant.
Positron
A particle of antimatter that is the antiparticle of the electron.
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
Power
Rate of transfer of energy = energy transferred / time taken
Pressure
The force per unit area that a gas or a liquid or a solid at rest exerts normally on (i.e. at right angles to ) a surface.
Pressure is measured in pascals (Pa) where 1 Pa = 1 M/m^2.
Pressure law
for a fixed mass of an ideal gas at constant volume, its pressure is directly proportional to its absolute temperature.
Principle of conservation of energy
In any change, the total amount of energy after the change is always equal to the total amount of energy before the change.
Proton
…
Radial field
A field in which the field lines are straight and converge or diverge as if from a single point.
Radian
….
Reactor core
The fuel rods, control rods, and the absorber rods of a nuclear reactor which together with the moderator substance are in a steel vessel through which the coolant (which is also the moderator in a PWR) is pumped.
Renewable energy
Energy from a source that is continually renewed.
e.g. Hydroelectricity, tidal power, geothermal power, solar power, wave power, and wind power.
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
Resonant frequency
the frequency of an oscillating system in resonance
Root mean square speed, c(rms)
square root of the mean value of the square of the molecular speeds of the molecules of a gas ..
Formula
Rutherford’s alpha particle scattering experiment
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 of the atom is located.
Satellite
A small object in orbit round a larger object
Satellite motion
…. Derive equations + Kepler’s Third Law
Simple electric motor
An electric motor with an armature consisting of a single coil of insulated wire.
SHM
Motion of an object where its acceleration is proportional to the displacement of the object from equilibrium and is always directed towards the equilibrium position.
3 derived equations
SHM Applications
- Simple pendulum
2. Mass spring system, vertical/horizontal
Sinusoidal curve
…
Specific heat capacity, c
Of a substance is the energy needed to raise the temperature of 1 kg of the substance of 1 K 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), where c is the specific heat capacity of the substance.
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.
Specific latent heat of vaporisation
For a substance is the energy needed to change the state of 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 fusion or vaporisation of the substance.
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 this distance it is a repulsive force.
Sublimation
The change of state when a solid changes to a vapour directly
Temperature
The degree of hotness of an object
Thermal energy
The 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
Time constant
The time taken for a quantity that decreases exponentially to decrease to 0.37 = 1/e of its original value. For the discharge of a capacitor through a fixed resistor, the time constant = RC
Time period
Time taken for one complete cycle of oscillations
Transformer
Converts the amplitude of an alternating pd to a different value.
Consists of two insulated coils, the primary coil and the secondary coil wound round a soft iron laminated core.
Step down transformer
Transformer in which the rms pd across the secondary coil is less than the rms pd applied to the primary coil.
Step up transformer
A transformer in which the rms pd of the secondary coil is greater than the rms pd applied to the primary coil.
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 turns.
Transformer efficiency
For an ideal transformer (i.e. one that is 100% efficient) the power output = ( secondary voltage x secondary current) = input power = (primary voltage x primary current).
Sources of transformer inefficiency
- Resistance heating of current in each coil
- The heating effect of eddy currents in the core
- Repeated magnetisation and demagnetisation of the core
Uniform circular motion
Motion of an object moving at constant speed along a circular path.
Uniform field
A region where the field strength is the same in magnitude and direction at every point in the field.
- electric field between two parallel fields
- Gravitational field over a region which is small compared to the scale of the Earth.
- Magnetic field inside a solenoid carrying a constant current that is uniform along and near the axis.
Velocity
Change of displacement per unit time
Work done
Work done is energy transferred by means of a force.
W = Fs cos theta
Wave particle duality
…
X Rays
…
