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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 momentsabout any pivot.

Work. The product of the force acting on a body and the displacement inthe direction of that force.

Joule Work done when a force of 1 Newton is moved a distance of 1metre.

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.

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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 oppositedirections 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 angleto the direction of travel of the wave.

Longitudinal Waves. A wave in which displacement is parallel to thedirection 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 thevibrations of the electric field.)

Wavefront. Line or surface in the path of a wave motion on which thedisturbances at every point have the same phase.

Principle of Superposition. The displacement of the resultant of twowaves is the sum of the displacements of the individual waves.

Interference. Interference of waves takes place when two or more wavesof the same type meet in space in such a way that there is a constantphase relationship between them and they are of similar amplitude andnot oppositely polarized.

Coherence. Two waves are coherent if there is a constant phasedifference between them and therefore they must have the samefrequency.

Diffraction. Spreading out of waves into a region of geometric shadowexperienced by waves as they pass through an aperture or around anobstacle. Diffraction is maximized if the gap/obstacle size is similar to thewavelength.

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 iscarrying a current of one Ampere and is perpendicular to the field.

Magnetic Flux Density . Is the magnetic force per unit current per unitlength 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 amonomer.

Amorphous Solid. An amorphous solid has no order the molecules are

randomly arranged.

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Pressure . The pressure acting on a surface is defined as the force actingper 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 beenremoved.

Plastic Behaviour. A material is said to be plastic if it does not return toits original size and shape when the load which has been deforming it isremoved.

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 limitof proportionality has not been exceeded the ratio stress/strain is aconstant 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 anelectric 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 isthe energy converted from electrical energy to other forms of energy whenunit charge passes between the two points or the electrical energy lost bythe charge per unit charge.

The Volt. The p.d. between two points when one Joule of work is done inmoving one Coulomb between the two points.

Electrical Resistance. defined in a conductor by the equation R=V/Ii.e. it is the ratio of potential difference across a conductor to the currentflowing through the conductor.

The Ohm. The resistance of a conductor through which a current of 1 ampis flowing when a p.d. across it is 1 Volt.

Ohm's Law. The current through an Ohmic Conductor is directlyproportional to the p.d. across it provided there is no change in thephysical conditions of the conductor i.e the temperature.

Resistivity. Defined by the equation = R / l ...in words the resistance xunit cross-sectional area per unit length.

Internal Resistance. The chemicals in a cell or the structure of a powerpack offer resistance when a current is drawn. This resistance is called theinternal resistance.

Electromotive Force EMF. of a cell is the energy converted intoelectrical energy from other forms when unit charge passes through it orthe amount of electrical energy gained by the charge per unit charge.

Terminal Potential Difference. The p.d. across the terminals of a powerpack 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.

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Photoelectric Effect . Emission of electrons from the surface of a metalirradiated by e-m radiation., usually ultraviolet.

The Photon. A quantum of e-m radiation (of energy E=hf, where h isPlancks constant).

Work Function Energy. The Work function energy of a surface is theminimum amount of energy that has to be given to an electron to releaseit 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 forone hour.

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A2 PHYSICS DEFINITIONS

Gravitational Potential Energy . The Energy that something possessesbecause 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. Newtons Law of Gravitation. F = GM 1M2 /r 2 where M 1 and M 2 are pointmasses and r is the separation between them. G = the universalgravitational constant = 6.67 x 10 -11 Nkg -2 m 2 .

Gravitational Field strength of a point mass. ...is proportional to themass and inversely proportional to the SQUARE of the distance from thepoint 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 isthe resultant of all the forces acting on the body.

Geostationary Orbits . Satellite with an orbital period of 24 hours abovethe equator and moving in the same direction as the earth is rotating.

Thus it stays above the same point on the Earths 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 equilibriumposition and always towards its equilibrium position. Acceleration is a = -(2 f) 2x.

Forced Oscillations. A system is undergoing forced oscillation if it isbeing forced to oscillate by some other system at the frequency of thatsystem

Damping . Oscillation of reducing amplitude owing to energy from thesystem being absorbed by the surroundings.

Resonance. A system which is being forced at its natural frequency is saidto be resonating its amplitude is maximum.

Electric field strength, E, is electric force per unit charge experiencedby a positive test charge in the field. (E at a point is proportional to thepotential gradient at the point i.e. the p.d. per unit distance.)

Electric field strength of a parallel plate field is the potentialdifference between the plates divided by their separation. E = V/d.

Coulombs Law. The electric force between two pint charges isproportional to the product of the charges and inversely proportional to thesquare of their separation. F = 1/4 0 x Q 1Q 2 /r 2 .

Electric field strength of a point charge = 1/4 0 x Q/r 2 . 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 themagnetic 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 theweber-turn.

Faradays Law. The magnitude of the emf induced in a coil is equal tothe rate of change of flux-linkage through the coli - in a conductor it isequal to the rate of cutting of magnetic flux.

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Lenzs Law. The direction of the emf is such as the current it inducesopposes the change causing it.

Internal Energy, U. The sum of the random potential and kineticenergies of the molecules of a system is called the internal energy and isdetermined 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 scalewhich does not depend on the properties of any substance. Its fixed pointsare absolute zero (0K) and the triple point of water (273.16K). Its unit isthe Kelvin.

Empirical Temperature Scale. A temperature scale which does dependon the properties of a particular substance. Its unit is the centigrade.

Celsius temperature. / o C = 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 thesubstance.

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-1

mol-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 nointeratomic forces in an ideal gas. (See any textbook for assumptionsmade 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.Avogadros number.

The Avogadro Constant - Numerically equal to the number of atoms inone mole N A = 6.02 x 10 23 .

The Relative Molecular Mass. Ratio of average mass of a molecule of asubstance 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 ThermalEquilibrium and so at the same temperature.

STP. Standard temperature and pressure (273K and 1.01 x 10 5 Pa). The average translational Kinetic Energy of the molecules of a gas

is proportional to its absolute temperature. ( U = 3/2kT where k isBoltzmanns constant and equals R/ N A, and T is Absolute Temperature.)

Nuclear Radiation. Emission of particles and/or waves from an unstablenucleus to enable it to achieve a more stable or lower energy state.

The Nuclear Atom. The positively charged core of an atom containingmost 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 nucleonnumbers.

Binding Energy. Energy required to separate nucleons in a nucleus toinfinite separation.

Binding Energy per Nucleon. Average energy which needs to besupplied to nucleus to remove a nucleon.

Nucleon or Mass Number. Number of neutrons and protons in thenucleus of an atom.

Proton or Atomic Number. Number of protons in the nucleus of anatom.

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 thenext second.

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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