AS Level Physics definitions

Scalar quantity: Magnitude onlyVector quantity:Magnitude and direction

Systematic errorConstant error (in all readings)Cannot be eliminated by averagingError in measuring instrumentRandom errorReadings scattered (equally) about true valueError due to observerCan be eliminated by averaging

Differences between the quantities distance and displacementDisplacement is a vector, distance is a scalarDisplacement is straight line between two points / distance is sum of lengths

Velocity:Rate of change of displacement

Acceleration:Rate of change of velocity

MassMeasure of body’s resistance/inertia to changes in velocity/motionConstantScalarWeightEffect of gravitational field on mass or force of gravityVariesVector

Linear momentum: Product of mass and velocity

Newton’s first law of motion:A body continues at constant velocity unless acted on by a resultant (external) force

Newton’s second law: (resultant) force = rate of change of momentum

Newton’s third law of motionForce on body A is equal in magnitude to force on body B (from A)Forces are in opposite directionsForces are of the same kind

Force: Rate of change of momentum

Elastic Collision:Total kinetic energy is conserved, Inelastic: loss of kinetic energy

Principle of conservation of momentumTotal/sum momentum before = total/sum momentum afterIn any closed system

MomentForce × perpendicular distanceOf force from pivot / axis / point

Principle of momentsThe sum of the clockwise moments about a point equals the sum of theAnticlockwise moments (about the same point)

Conditions necessary for a body to be in equilibriumNo resultant force (in any direction)No resultant moment (about any point)

Centre of gravityPoint at which (whole) weight (of body)Appears / seems to act

TorqueProduct of one of the forces and the distance between forcesThe perpendicular distance between the forces

Couple: (Magnitude of) one force × perpendicular distance between the two forces

Work doneProduct of force and distance moved(By force) in the direction of the force

Potential energy:Stored energy available to do workGravitational: Due to height/position of mass OR distance from mass OR moving mass from one point to anotherElastic: Due to deformation/stretching/compressingElectrical: Charge moved due to work done in electric field

Internal energySum of (random) kinetic and potential energiesOf the atoms/molecules of the substance

Power: Work done per unit time / energy transferred per unit time / rate of work done

Density: Mass/Volume

Pressure: Force / area

Brownian motionHaphazard / random / erratic / zigzag movement

Of (smoke) particles

Similarities between the processes of evaporation and boiling(Phase) change from liquid to gas / vapourThermal energy required to maintain constant temperature

Differences between the processes of evaporation and boilingEvaporation takes place at surfaceBoiling takes place in body of the liquidEvaporation occurs at all temperaturesBoiling occurs at one temperature

CrystallineAtoms / ions / particles in a regular arrangement / latticeLong range order / orderly pattern(Lattice) repeats itselfPolymerLong chain molecules / chains of monomersSome cross-linking between chains / tangled chainsAmorphousDisordered arrangement of molecules / atoms / particlesAny ordering is short-range

Assumptions of the simple kinetic model of a gasLarge number of molecules / atoms / particlesMolecules in random motionNo intermolecular forcesElastic collisionsTime of collisions much less than time between collisionsVolume of molecules much less than volume of containing vessel

Difference in densities in solids, liquids and gasesDensity in solids and liquids similarSpacing in solids and liquids about the sameDensity in gases much less as spacing in gases much greater

Hooke’s law:Extension is proportional to force / load

Elastic limit:Point beyond which material does not return to the original length / shape / sizeWhen the load / force is removed

Elastic deformationChange of shape / size / length / dimensionWhen (deforming) force is removed, returns to original shape / size

Plastic deformation:When the load is removed then the wire / body object does not return to its original shape / Length

Stress: Force / (cross-sectional) area

Strain: Extension / original length or change in length / original length

Young modulus: Stress / strain

Ultimate tensile stressMaximum force / original cross-sectional areaWire is able to support / before it breaks

Transverse waves have vibrations that are perpendicular / normalTo the direction of energy travel

Longitudinal waves have vibrations that are parallelTo the direction of energy travel

PolarizationVibrations are in a single directionApplies to transverse wavesNormal to direction of wave energy travelNormal to direction of wave propagation

WavelengthDistance moved by wave energy / wavefront during one cycle of the sourceOr minimum distance between two points with the same phase or between adjacent crests or trough

Frequency of a progressive wave: Number of oscillations per unit time of the source / of a point on the wave

Speed of a progressive wave: Speed at which energy is transferred / speed of wavefront

Principle of superposition(When the waves meet) the resultant displacement is the sum of theDisplacements of each wave

Diffractionof a waveWhen a wave passes through a slit / by an edgeThe wave spreads out / changes direction

InterferenceWhen two (or more) waves meet (at a point)There is a change in overall intensity / displacement

Distinct features of waves that are common to all regions of the electromagnetic spectrumAll same speed in a vacuum /all travel in a vacuumTransverse/can be polarisedUndergo diffraction/interference/superpositionCan be reflected/refractedShow properties of particles

Oscillating electric and magnetic fieldsTransfer energy/progressiveNot affected by electric and magnetic fields

Coherent: Constant phase difference (between waves)

Conditions that must be satisfied in order that two waves interfereBoth transverse/longitudinal/same typeMeet at a pointSame direction of polarization

Diffraction of a waveWhen a wave (front) is incident on an edgeOr an obstacle/slit/gapWave ‘bends’ into the geometricalShadow/changes direction/spreads

Node: Position (along wave) where amplitude of vibration is a minimum

Antinode:Position (along wave) where amplitude of vibration is a maximum

Features of a stationary wave that distinguish it from a progressive waveNo energy transferAmplitude varies along its length/nodes and antinodesNeighbouring points (in inter-nodal loop) vibrate in phase

Principle of superposition to explain the formation of a stationary waveTwo waves travelling (along the same line) in opposite directions overlap/meetSame frequency / wavelengthResultant displacement is the sum of displacements of each wave /Produces nodes and antinodes

Electric field strength: Force per unit positive charge (acting on a stationary charge)

Electric field:Region/area where a charge experiences a force

Electric charge: Current × time

Coulomb: Charge flowing per second pass a point at which the current is one ampere.

Electric current: Movement/flow of charged particles

Electric potential difference: Work done per unit charge (transferred)

Electromotive force (e.m.f.):Energy converted from chemical to electrical when charge flows through cell or round complete circuit

Volt: Potential difference between two points in a circuit in which one joule of energy is converted from electrical to non-electrical energy when one coulomb passes from one point to

the other.

Electromotive force (e.m.f.) of a cell and the potential differenceBoth measure (energy / work) / chargeFor e.m.f., transfer of chemical energy to electrical energyFor p.d., transfer of electrical energy to thermal energy / other forms

Electrical resistance: Potential difference / current

Internal resistance: (resistance of the cell) causing loss of voltage or energy loss in cell

Ohm: Volt / ampere

Ohm’s Law: The potential difference across a component is proportional to the current in it providing physical conditions stay constant

Kirchhoff’s first law: Sum of currents into a junction = sum of currents out of junctionLinked to conservation of charge

Kirchhoff’s second law:Sum of e.m.f.’s = sum of p.d.’s around a loop/circuitLinked to conservation of energy

Radioactive decayNucleus emits α-particles or β-particles and/or γ-radiationTo form a different / more stable nucleus

Spontaneous radioactive decayThehalf-life / count rate / rate of decay / activity is the same no matter whatExternal factors / environmental factors or two named factors such asTemperature and pressure changes are applied

Random radioactive decayThe observations of the count rate / count rate / rate of decay / activity / radioactivity during decay shows variations / fluctuations

IsotopeDifferent forms of same elementNuclei have same number of protonsDifferent numbers of neutrons (in the nucleus)

Quantities that are conserved in a nuclear reactionProton numberNucleon numberMass-energy

Deduction from the fact that most α-particles were deviated through angles of less than 10°Nucleus is smallIn comparison to size of atom

Deduction from the fact that a very small proportion of the α-particles was deviated through angles greater than 90°Nucleus is massive/heavy/denseAnd charged

α-particle and a β-particleα-particle: helium nucleus or contains 2 protons + 2 neutronsΒ-particle: electronΑ speed < β speedΑ discrete values of speed/energy, β continuous spectrum Either α ionising power >> β ionizing powerOr α range << β rangeα positive, β negativeα mass > β mass

Properties of α-particlesRange is a few cm in air/sheet of thin paperSpeed up to 0.1 cCauses dense ionisation in airPositively charged 2eMass 4uConstant energyAbsorbed by thin paper or few cm of air (3 cm → 8 cm)Highly ionizingDeflected in electric/magnetic fields

Properties of β-particlesCan be deflected by electric and magnetic fields or negatively charged /Absorbed by few (1 – 4) mm of aluminum / 0.5 to 2 m or metres for range in air /Speed up to 0.99c / range of speeds / energies

Ahmed Aqdam Tariq