Paper 2 Definitions Flashcards
Absolute zero
The lowest possible temperature of a system, where no heat remains and the particles in the system have no kinetic energy
Avogadro constant
The number of particles that make up one mole of any gas
Boltzmann constant
A constant relating the average kinetic energy of the particles in a gas to the gas temperature
Boyles law
The pressure of an ideal gas is inversely proportional to its volume when held at constant temperature
Brownian motion
the random motion of particles
Charles law
The volume of an ideal gas is directly proportional to its absolute temperature when held at constant pressure
Ideal gas
A gas that meets all the gas assumptions. Follows all the gas laws and cannot be liquified
Internal energy
The sum of the randomly distributed kinetic and potential energies of the particles in a given system
Molar gas constant
A fundamental constant, used in the ideal gas law
Molar mass
The mass of one mole of a substance
Pressure law
The pressure of an ideal gas is directly proportional to its absolute temperature, when the volume is fixed
Specific heat capacity
The amount of energy required to increase the temperature of 1kg of a substance by 1 Kelvin
Specific latent heat
The amount of energy required to change the state of 1kg of a substance without raising the temperature
State changes
During a state change the potential energy of the system is changing but the kinetic energy is not
Capacitance
The charge stored per unit pd in a capacitor
Capacitor
An electrical component that stores charge. A parallel-plate capacitor is made of two parallel conducting plates with an insulator between them
Coulombs law
The size of the force that acts between two point charges is proportional to the product of their charges and inversely proportional to the square of their separation.
Cyclotron
A particle accelerator made up of two D shaped electrodes positioned opposite each other. The electric field changes direction each time a particle moves from one electrode to the other causing the particle to accelerate
Electromagnetic Induction
When an emf is induced in a wire/conducting rod
when it is moved relative to a magnetic field
Equipotential
A surface of constant potential. No work is done by the field when an object
moves along an equipotential.
Escape Velocity
The minimum velocity required by an object to be able to escape a
gravitational field of a mass when projected vertically from its surface.
Faraday’s Law
The magnitude of the induced emf is equal to the rate of change
of flux linkage through the circuit.
Field Line / Line of Force
A line representing the path that a north pole (magnetic field), positive charge (electric field) or mass (gravitational field) would take when placed within the
field.
Force Field
An area in which an object will experience a non-contact force
Geostationary Satellite
A satellite that orbits above the equator with a 24 hour period, so it
will always remain above the same position on the Earth. They orbit approximately 36,000km
above the surface of the Earth.
Gravitational Field
A region surrounding a mass in which any other object with mass will experience an attractive force.
Gravitational Field Strength
The force per unit mass exerted on a small test mass placed
within the field.
Gravitational Potential, V (at a point in the field)
The work done per unit mass required to move a small test mass from infinity to that point.
Gravitational Potential Energy
The component of an object’s energy due to its position in a gravitational field.
Kepler’s Third Law
The square of an object’s orbital period (T) is directly proportional to the
cube of its orbital radius (r) – T2 ∝ r3
Lenz’s Law
An induced current is always in a direction so as to oppose the change that caused it
Magnetic Field
A region surrounding a magnet or current-carrying wire that will
exert a force on any other magnet or current-carrying wire placed within it
Magnetic Flux, ϕ
A value which describes the magnetic field or field lines passing through
an area. It is the product of magnetic flux density and the perpendicular area it passes
through.
Magnetic Flux Density, B
The force per unit current per unit length on a current-carrying wire placed at 90º to the field lines. Sometimes also referred to as the magnetic field
strength.
Magnetic Flux Linkage, Nϕ
The magnetic flux multiplied by the number of turns, N, of the coil.
Motor Effect
When a current-carrying wire is placed within a magnetic field (non-parallel to the field lines) and experiences a force perpendicular to both the wire and the field lines
Permittivity of free space, ε0
A measure of the ability of a vacuum to allow an electric field to pass through it.
Polarised
An atom/molecule becomes polarised when an external electric field causes the negative electron cloud to be shifted in the opposite direction to the positive nucleus – the charges are pulled in opposite directions. (This is what happens to the molecules of the dielectric in a capacitor).
Potential Gradient
The change of potential per metre at a point in the field.
Radial Field
A field in which the field lines are all directed towards a single point (e.g. the
centre of a planet or a point charge).
Relative Permittivity
The ratio of charge stored in a capacitor with the dielectric to charge
stored without the dielectric. Also sometimes referred to as the dielectric constant.
Step-down Transformer
A device made of two insulated wires coiled around an iron core in which the output voltage is smaller than the input voltage due to the secondary coil having fewer turns than the primary coil.
Step-up Transformer
A device made of two insulated wires coiled around an iron core in which the output voltage is greater than the input voltage due to the secondary coil having more turns than the primary coil.
Synchronous Orbit
An orbit in which the period of the orbit is equal to the rotational period of the object that it is orbiting.
Time Constant
The time taken for a capacitor to discharge to 37% (e-1) of its initial charge. The time constant is equal to the product of the capacitance and the resistance of the fixed resistor (that the capacitor is being discharged through).
Uniform Field
A field in which all of the field lines are parallel and equally spaced – field strength is equal in all areas of the field.
Activity
The rate of decay of the radioactive nuclei in a given isotope. It is proportional to the total number of nuclei in the sample and is measured in Becquerels.
Alpha Decay
The emission of an alpha particle (2 protons and 2 neutrons) from an unstable nucleus (usually one with too much mass) to make it more stable. Alpha radiation is strongly ionising and is stopped by a few centimetres of air or a sheet of paper.
Atomic Mass Unit
A unit used to express atomic masses. One AMU is equal to
the one twelfth of the mass of a carbon atom.
Background Radiation
Radiation that is found in small quantities all around us. It originates from natural sources such as rocks and cosmic rays as well as
man-made sources such as nuclear accidents and medical sources.
Beta Decay
The emission of a beta particle when a proton turns into a neutron (or vice versa) in an unstable nucleus. Beta minus radiation is weakly ionising. Beta plus radiation is immediately annihilated by electrons.
Binding Energy
The amount of energy required to split a nucleus into all its
separate constituent nucleons. It is equivalent to the mass defect.
Chain Reaction
The process of the neutrons released by a fission reaction
inducing further fissile nuclei to undergo fission.
Closest Approach
A method of estimating a nuclear radius by firing a alpha particle at it. It involves calculating the distance at which all the alpha particle’s
kinetic energy is converted to electric potential energy
Contamination
The introduction of radioactive material to another object. The
object is consequently radioactive.
Control Rods
Rods found in nuclear reactors to absorb neutrons and control the
rate of reaction. They can be raised or lowered depending on the rate required.
Coolant
A substance that passes through nuclear reactors and is responsible for removing heat from the core. This heat is then used to generate energy.
Critical Mass
The smallest mass of fissile material required in a fission reactor
for a chain reaction to be sustained.
Electron Capture
A process that occurs in proton-heavy nuclei, in which an electron is drawn into the nucleus, causing a proton to transition into a neutron. An electron neutrino is also produced.
Fission
The splitting a nucleus, to form two smaller daughter nuclei, neutrons and energy.
Fusion
The joining of two smaller nuclei to form a larger nucleus and to release
energy.
Gamma Decay
The emission of gamma rays from an unstable nucleus that has too much energy. Gamma radiation is only very weakly ionising but requires several centimetres of lead to be stopped.
Half-Life
The average time it takes for the number of radioactive nuclei in a
sample to halve.
Inverse Square-Law
A law that governs the intensity of gamma radiation. It means that the intensity of radiation at any point is inversely proportional to the
square of the distance from its source.
Irradiation
The exposure of an object to radiation. The exposed object does not become radioactive.
Mass Defect
The difference in mass between a nucleus and the sum of the
masses of its constituent nucleons.
Moderator
A material in nuclear reactors that absorbs energy from fast moving neutrons, to slow them down to speeds that can be absorbed by fissile neutrons to induce fission.
Radioactive Dating
The use of radioactive isotopes with known half-lives to date
objects. The isotope that is usually used is Carbon-14.
Radioactive Waste
The waste produced from the products of fission reactions. Since the waste is unstable and radioactive, it must be stored and handled carefully.
Random Nature of Radioactive Decay
Radioactive decay is random - you cannot predict when a nucleus will decay or which nucleus will decay next.
Rutherford Scattering
An experiment involving firing alpha particles at a thin gold foil and observing their deflections. It showed the existence and nature of the nucleus.
