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					                                 AS Definitions


   Scalar. Physical Quantity with magnitude only - no direction.
   Vector. Physical quantity with magnitude and direction.
   Coplanar. In the same plane.
   Systematic Error or Uncertainty. Error in which measurements are consistently
    too high or too low due to the apparatus or the way it is used.
   Random Error or Uncertainty. Statistical error with some readings being too high
    or too low caused by a lack of care or lack of sensitivity of measuring instrument.
   Displacement. Distance in a particular direction
   Speed. Distance travelled /Time taken
   Velocity. Rate of change of displacement
   Acceleration Rate of change of velocity
   Force. The force on a body is the rate of change of momentum.
   The Newton. There is a net force of 1 newton acting if a one kilogram object has
    an acceleration of one metre per second per second.
   Upthrust. The apparent loss of weight of a body immersed in a fluid and equal to
    the weight of the fluid displaced.
   Viscosity. The internal friction of a fluid caused by molecular attraction.
   Friction. The resistance to motion between two surfaces that touch.
   Mass. A property of a body which resists change in motion.
   Weight. The effect of gravitational field on a mass.
   Inertia/Inertial Mass. Resistance to change in motion of a body.
   Centre of Gravity. The single point through which the weight may be assumed to
    act.
   Moment of a force or Torque. The product of the force and the perpendicular
    distance from the pivot to the line of action of the force.
   Couple. Two forces which act on a body and are equal in magnitude and opposite in
    direction separated by a perpendicular distance.
   Torque of a couple. The product of ONE of the forces and the perpendicular
    distance between them.
   Equilibrium. A system is in equilibrium if there is no resultant force and no resultant
    torque on it.
   Principle of Moments. If a body is in equilibrium the sum of the anticlockwise
    moments on it equals the sum of the clockwise moments about any pivot.
   Work. The product of the force acting on a body and the displacement in the
    direction of that force.
   Joule Work done when a force of 1 Newton is moved a distance of 1 metre.
   Power. Power is defined as the rate of work done or energy transferred.
   Watt. The power when one joule per second of work is done/energy transferred.
   Kinetic Energy. The Energy that something possesses because of its motion.
   Gravitational Potential Energy. The Energy that something possesses because of
    its position in a gravitational field.
   Gravitational Field Strength. The Force per unit mass felt by matter in a
    gravitational field.
   Amplitude. Displacement from equilibrium position
   Period. Time taken for one complete oscillation.
   Frequency. Number of oscillations per second.
   Hertz. 1 Hz is one cycle per second.
   Phase Difference. The angular separation between two parts of a wave. It can be
    expressed as the fraction of a cycle x 360o.
   In Phase. When two waves are in phase they have no phase difference.
   Anti Phase. Two waves that are 180 o out of phase.
   Refraction. The bending of waves that occurs at a boundary when they enter a
    medium where their velocity changes.
   Refractive Index. Ratio of velocity of light in a vacuum to velocity of light in
    medium.
   Critical Angle. Angle of incidence for which angle of refraction is 90° when light is
    travelling into a less dense medium.
   Total Internal Reflection. If the angle of Incidence exceeds the critical angle there
    is Total Internal Reflection.
   Progressive Wave. A wave where there is net transfer of Energy.
   Standing Wave. A wave in which there is NO net transfer of Energy. A standing
    wave is formed when two identical waves travelling in opposite directions meet
   Wave Intensity. The intensity of the wave is proportional to the square of the
    Amplitude. It is the rate of energy per unit area.
   Transverse Waves. A wave in which displacement moves at a right angle to the
    direction of travel of the wave.
   Longitudinal Waves. A wave in which displacement is parallel to the direction of
    travel of the wave.
   Wavelength. Distance between any part of the wave and the nearest part In Phase
    with it.
   Polarization. If all the vibrations of a transverse wave are in a single plane the
    wave is said to be plane polarized. (In an e-m wave it is the vibrations of the electric
    field.)
   Wavefront. Line or surface in the path of a wave motion on which the disturbances
    at every point have the same phase.
   Principle of Superposition. The displacement of the resultant of two waves is the
    sum of the displacements of the individual waves.
   Interference. Interference of waves takes place when two or more waves of the
    same type meet in space in such a way that there is a constant phase relationship
    between them and they are of similar amplitude and not oppositely polarized.
   Coherence. Two waves are coherent if there is a constant phase difference between
    them and therefore they must have the same frequency.
   Diffraction. Spreading out of waves into a region of geometric shadow experienced
    by waves as they pass through an aperture or around an obstacle. Diffraction is
    maximized if the gap/obstacle size is similar to the wavelength.
   Nodes. Positions of no displacement in standing waves.
   Anti-nodes. Positions of maximum displacement in standing waves.
   The Tesla. The magnetic Flux Density of a field in which a force of one Newton acts
    on a one metre length of a conductor in the field which is carrying a current of one
    Ampere and is perpendicular to the field.
   Magnetic Flux Density. Is the magnetic force per unit current per unit length of
    conductor in the field which is lying at right angles to the field.
   Density. The Density of a substance is the ratio of its mass to its volume.
   Crystalline Solid. In a crystalline solid the atoms or molecules are arranged in a
    regular 3-dimensional array.
   Non-crystalline. In a non-crystalline solid the atoms or molecules are not arranged
    in a regular 3-dimensional array.
   Metallic Solid. Metals comprise an array of positive ions in a sea of electrons.
   Polymer. A polymer has large molecules in the form of long chains, each chain
    consists of a large number of small molecules and is called a monomer.
   Amorphous Solid. An amorphous solid has no order – the molecules are randomly
    arranged.
   Pressure. The pressure acting on a surface is defined as the force acting per unit
    cross-sectional area.
   Stress. Force per unit cross-sectiional area.
   Strain. Change in length divided by original length.
   Elastic Behaviour. A material is said to be elastic if it returns to its original size and
    shape when the load which is deforming it has been removed.
   Plastic Behaviour. A material is said to be plastic if it does not return to its original
    size and shape when the load which has been deforming it is removed.
   Ductile. A ductile material is one which can be permanently stretched.
   Stiffness. The resistance which a material offers to having its size or shape
    changed.
   Elastic Limit. The maximum load which a body can experience and still retain its
    original size and shape once the load has been removed.
   Breaking Stress. Stress at which material breaks.
   Ultimate tensile strength. Maximum stress which can be applied to a material
    without causing it to break.
   Brittleness. A brittle material cannot be permanently stretched – it breaks soon
    after its elastic limit has been reached.
   Young Modulus. Provided that the stress is not too high and that the limit of
    proportionality has not been exceeded the ratio stress/strain is a constant for a given
    material and is known as the Young modulus.
   Charge. The property of a body which causes it to feel a force in an electric field.
   Charging by friction. Separation of charges by rubbing.
   Charging by Induction. Separation of charge by position in an Electric Field.
   Coulomb. The charge which flows past any one point in any one second when one
    ampere of current flows.
   Electric Current. Flow of charged particles.
   The Ampere is defined in terms of the magnetic force between two parallel current
    carrying conductors.
   Potential Difference. The p.d. between two points in an electric field is the energy
    converted from electrical energy to other forms of energy when unit charge passes
    between the two points or the electrical energy lost by the charge per unit charge.
   The Volt. The p.d. between two points when one Joule of work is done in moving
    one Coulomb between the two points.
   Electrical Resistance. …defined in a conductor by the equation R=V/I i.e. it is the
    ratio of potential difference across a conductor to the current flowing through the
    conductor.
   The Ohm. The resistance of a conductor through which a current of 1 amp is flowing
    when a p.d. across it is 1 Volt.
   Ohm's Law. The current through an Ohmic Conductor is directly proportional to the
    p.d. across it provided there is no change in the physical conditions of the conductor
    i.e the temperature.
   Resistivity. Defined by the equation =Rl ...in words the resistance x unit cross-
    sectional area per unit length.
   Internal Resistance. The chemicals in a cell or the structure of a power pack offer
    resistance when a current is drawn. This resistance is called the internal resistance.
   Electromotive Force EMF. …of a cell is the energy converted into electrical energy
    from other forms when unit charge passes through it or the amount of electrical
    energy gained by the charge per unit charge.
   Terminal Potential Difference. The p.d. across the terminals of a power pack or
    cell. It is equal to the e.m.f. when no current is drawn.
   Quantisation of Charge. Electric charge can never exist in fractions of “e”.
   Photoelectric Effect. Emission of electrons from the surface of a metal irradiated
    by e-m radiation., usually ultraviolet.
   The Photon. A quantum of e-m radiation (of energy E=hf, where h is Planck’s
    constant).
   Work Function Energy. The Work function energy of a surface is the minimum
    amount of energy that has to be given to an electron to release it from the surface.
   Threshold Frequency. Minimum value of frequency of incident radiation necessary
    to cause Photoelectric emission.
   The Electronvolt. A unit of energy equal to the kinetic energy gained by an electron
    in being accelerated through a potential difference of 1 volt.
   De Broglie Wavelength. Any particle of momentum mv has an associated
    wavelength, the de Broglie wavelength, given by =h/mv.
   The kilowatt-hour. A unit of electrical energy equal to the energy transferred
    when an electrical device of power one kilowatt operates for one hour.
                        A2 PHYSICS DEFINITIONS

   Gravitational Potential Energy. The Energy that something possesses because of
    its position in a gravitational field.
   Field of force. A region in space in which an object experiences a force.
   Gravitational Field Strength. The Force per unit mass felt by matter in a
    gravitational field.
   Newton’s Law of Gravitation. F = GM1M2/r2 where M1 and M2 are point masses
    and r is the separation between them. G = the universal gravitational constant =
    6.67 x 10-11 Nkg-2m2.
   Gravitational Field strength of a point mass. ...is proportional to the mass and
    inversely proportional to the SQUARE of the distance from the point mass.
   Angular Displacement. Angle turned through IN A SPECIFIED DIRECTION.
   Angular Velocity. Rate of change of angular displacement.
   Centripetal Acceleration. The acceleration experienced by a body moving in a
    circle which always acts towards the centre of the circle. a = v 2/r
   Centripetal Force. The force which causes centripetal acceleration. It is the
    resultant of all the forces acting on the body.
   Geostationary Orbits. Satellite with an orbital period of 24 hours above the
    equator and moving in the same direction as the earth is rotating. Thus it stays
    above the same point on the Earth’s surface.
   Free Oscillations. An oscillating system which is not forced to move.
   Simple Harmonic motion. A system oscillates with SHM if a restoring force acts on
    it proportional to its displacement from its equilibrium position and always towards its
    equilibrium position. Acceleration is a = - (2f)2x.
   Forced Oscillations. A system is undergoing forced oscillation if it is being forced to
    oscillate by some other system at the frequency of that system
   Damping. Oscillation of reducing amplitude owing to energy from the system being
    absorbed by the surroundings.
   Resonance. A system which is being forced at its natural frequency is said to be
    resonating – its amplitude is maximum.
   Electric field strength, E, is electric force per unit charge experienced by a positive
    test charge in the field. (E at a point is proportional to the potential gradient at the
    point i.e. the p.d. per unit distance.)
   Electric field strength of a parallel plate field is the potential difference
    between the plates divided by their separation. E = V/d.
   Coulomb’s Law. The electric force between two pint charges is proportional to the
    product of the charges and inversely proportional to the square of their separation. F
    = 1/40 x Q1Q2/r2.
   Electric field strength of a point charge = 1/40 x Q/r2.
   Capacitance. Ratio of charge stored to potential difference across a capacitor.
   Farad. The capacitance of a capacitor which stores one Coulomb of charge when
    there is one Volt across it.
   Magnetic Flux. …through a region is a measure of the number of magnetic field
    lines passing through the region. It is defined as the magnetic flux density normal to
    the area x the area.  = BA
   The Weber. 1 weber = 1 tesla-metre squared.
   Magnetic Flux Linkage. The product of the number of turns and the flux through a
    coil. It is the magnetic flux threading the coil. Its unit is the weber-turn.
   Faraday’s Law. The magnitude of the emf induced in a coil is equal to the rate of
    change of flux-linkage through the coli - in a conductor it is equal to the rate of
    cutting of magnetic flux.
   Lenz’s Law. The direction of the emf is such as the current it induces opposes the
    change causing it.
   Internal Energy, U. The sum of the random potential and kinetic energies of the
    molecules of a system is called the internal energy and is determined by the state of
    the system.
   Temperature. The temperature of a body is a measure of how hot it is i.e. the
    mean kinetic energy of its molecules NOT how much heat it contains. For an ideal
    gas it is proportional to the internal energy of the gas
   Absolute or Thermodynamic Temperature Scale. A temperature scale which
    does not depend on the properties of any substance. Its fixed points are absolute
    zero (0K) and the triple point of water (273.16K). Its unit is the Kelvin.
   Empirical Temperature Scale. A temperature scale which does depend on the
    properties of a particular substance. Its unit is the centigrade.
   Celsius temperature. /oC = T/K – 273.15.
   Specific Heat Capacity. The Specific Heat Capacity of a substance is the heat
    required to produce unit temperature rise in unit mass of the substance.
   The Equation of State or Ideal Gas Equation. Relates the pressure, volume,
    absolute temperature and number of moles of an Ideal gas i.e. pV = nRT, where R
    = molar gas constant 8.31 Jkg-1mol-1.
   An Ideal Gas. Defined as one which obeys the Ideal gas Equation exactly. It has
    only internal kinetic energy since it is assumed there are no interatomic forces in an
    ideal gas. (See any textbook for assumptions made about ideal gases).
   The Mole. The amount of a substance which contains the same number of
    molecules or elementary units as there are atoms in 12g of Carbon-12. i.e.
    Avogadro’s number.
   The Avogadro Constant - Numerically equal to the number of atoms in one mole
    NA = 6.02 x 1023.
   The Relative Molecular Mass. Ratio of average mass of a molecule of a substance
    to one twelfth the mass of a Carbon-12 atom.
   The Molar Mass. The mass per mole of a substance.
   Thermal Equilibrium. If two bodies are in thermal contact and there is no net flow
    of heat energy between them they are said to be in Thermal Equilibrium and so at
    the same temperature.
   STP. Standard temperature and pressure (273K and 1.01 x 105 Pa).
   The average translational Kinetic Energy of the molecules of a gas is
    proportional to its absolute temperature. ( U = 3/2kT where k is Boltzmann’s
    constant and equals R/ NA, and T is Absolute Temperature.)
   Nuclear Radiation. Emission of particles and/or waves from an unstable nucleus to
    enable it to achieve a more stable or lower energy state.
   The Nuclear Atom. The positively charged core of an atom containing most of the
    mass of the atom. It is surrounded by orbiting electrons.
   Nucleon. An inhabitant of the nucleus i.e. protons and neutrons.
   Isotopes. Nuclides with the same proton number but different nucleon numbers.
   Binding Energy. Energy required to separate nucleons in a nucleus to infinite
    separation.
   Binding Energy per Nucleon. Average energy which needs to be supplied to
    nucleus to remove a nucleon.
   Nucleon or Mass Number. Number of neutrons and protons in the nucleus of an
    atom.
   Proton or Atomic Number. Number of protons in the nucleus of an atom.
   Activity. The rate of decay of a radioactive nuclide.
   Decay Constant. Ratio of activity to the number of undecayed nuclei in a nuclide.
    =A/N It represents the probability of a nucleus decaying in the next second.
   Half Life. Time taken for half the undecayed nucleii in a sample to decay.
   Parent Nucleus. Emitting nucleus.
   Daughter Nucleus or decay product. New nucleus formed when decay occurs

				
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