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Cambridge A Level Physics: Definitions
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Cambridge A Level Physics
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AS Level Physics Terms & Concepts
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Lvl Ch
Term
Definition
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AS 1
Derived Units
Some combination of the base units. The base units may be multiplied together or divided by
one another, but never added or subtracted.
AS 1
Homogeneous
Units
When each term has the same base units, the equation is said to be homogeneous or
‘balanced’.
AS 1
Scalar
A quantity that has magnitude/size
AS 1
Vector
A quantity that has magnitude/size and direction
AS 1
Accuracy
How close a reading is to its true value. When readings are accurate, the peak / average
value moves towards the true value
AS 1
Precision
Smallest change in value that can be measured by an instrument. OR Spread of values /
measurements (scatter between each data is relatively small/ lines are closer together /
sharper peak)
AS 1
Random errors
Readings have positive and negative values around the peak value / values are scattered /
wide range. To reduce errors, take several readings to get an average value.
AS 1
Systematic Error
The average / peak is not the true value / the readings are not centred around the true value.
Look/check for zero error to avoid systematic error.
AS 1
Uncertainty
The range of value within which a measurement is likely to be in.
AS 2
Acceleration
(vector)
Rate of change of velocity.
AS 2
Displacement
(vector)
is the straight line distance between start and finish points (in that direction) / minimum
distance
AS 2
Distance (scalar) is the actual path travelled
AS 2
Free Fall
The downward motion of an object under the influence of force of gravity with a constant
acceleration (g = 9.81 ms-2).
AS 2
Projectile motion
Objects acted upon by a force with vector at perpendicular to its horizontal velocity. Asume
zero frictional forces. Tracjectory of the object will result in a parabola.
AS 2
Speed (scalar)
Distance travelled per unit time taken
AS 2
Terminal velocity Constant speed of object when resultant force is zero due to large air resistance.
AS 2
Velocity (vector) Rate of change of displacement
AS 3
Conservation Of Total momentum of (an isolated) system (of interacting bodies) remains constant, provided
Momentum
there are no resultant external forces (e.g. friction)
AS 3
Total momentum and total Kinetic Energy of a system is conserved. Relative speed of
Elastic Collisions
approach is equal to the relative speed of separation
AS 3
Force
Rate of change of momentum
AS 3
Force
It is defined as the rate of change of momentum of a body
► 2011 (1)
AS 3
Impulse
It is the product of a force & the time during which the force is applied.
► 2010 (1)
AS 3
Inelastic
Collisions
Total momentum of a system is conserved, but the total Kinetic Energy is not conserved.
Speed before impact is not equal to speed
AS 3
Linear
Momentum
Product of an object's mass & velocity, with its direction always being the same as the
direction of velocity.
AS 3
Mass
It is a measure of inertia of a body or the property of a body that resists change in motion
AS 3
Newton’s 1st
Law
A body remains at rest or constant velocity unless acted on by a resultant (external) force
AS 3
Newton’s 2nd
Law
The (resultant) force is proportional to the rate of change of momentum
AS 3
Newton’s 3rd
Law
If one body exerts a force on another, it will experience a force by the other body, which is
equal in magnitude & opposite in direction. Both forces are the of the same kind.
AS 3
Weight
Weight is the force due to the gravitational field
AS 4
Centre Of Gravity
The point on an object at which the entire weight of the body seemingly acts. It is the point at
which the Earth actually applies the pull of gravity.
AS 4
Density
Amount of mass per unit volume of a substance.
AS 4
Equilibrium
Net / resultant force and moment is zero (OR sum of clockwise moments = sum of
anticlockwise moments). If the triangle of forces is ‘closed’ then there is no resultant force
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Cambridge A Level Physics: Definitions
and the object is in equilibrium.
AS 4
Moment / Torque Product of the force and the perpendicular distance to the pivot
AS 4
Pressure
The perpendicular/normal force applied per unit area
AS 4
Principle Of
Moments
The sum of the clockwise moments about a point equals the sum of the anticlockwise
moments (about the same point)
AS 4
Torque Of A
Couple
Product of one of the forces and perpendicular distance between forces. (The turning effect
caused by two equal & opposite forces when their line of actions are different.)
AS 4
Upthrust
It is the resultant force on a submerged object due to pressure difference between the higher
pressure at the bottom of the object and the lower pressure at the top of the object immersed
in a fluid.
AS 5
Energy
It is the stored ability to do work.
AS 5
Work Done
Product of a force & the distance moved in the direction of the force.
AS 5
Gravitational
Energy stored due to height/position of mass
Potential Energy
AS 5
Internal Energy
It is the total of the microscopic Kinetic & Potential energies of particles of a material.
AS 5
Kinetic Energy
Energy of an object due to its motion.
AS 5
Potential Energy Energy stored by an object to do work
AS 5
Elastic Potential
Energy stored due to deformation or change in shape of an object
Energy
AS 5
Electric potential
Potential energy (stored) when charge moved due to work done in electric field
energy
AS 5
Power
Rate of work done
AS 5
Efficiency
The fraction of the useful power output obtained from the total power input.
AS 6
Brittle Materials
Materials which do not undergo plastic deformation. Force proportional to extension until it
breaks
AS 6
Ductile Materials
Materials which undergo plastic deformation after a considerable elastic deformation. Initially
force proportional to extension then a large extension for small change in force
AS 6
Elastic
Deformation
Object returns to its original length (zero extension) when load is removed
AS 6
The area under such a graph is the work done in stretching a material. For the straight-line
Force-Extension portion of the graph, it is a measure of the elastic potential energy stored by the material,
Graph
provided that the graph for decreasing loads is the same as that for increasing loads. It is
also known as strain energy.
AS 6
Hooke's Law
Force/load is proportional to extension/compression if proportionality limit is not exceeded.
AS 6
Necking
When a sufficiently large force is applied, localized narrowing occurs at weak points, & the
wire eventually breaks at one of these points.
AS 6
Plastic
Deformation
Wire/body object does not return to its original shape / length when load is removed
AS 6
Polymeric
Materials
Materials which can undergo great strain, & deform to a very great degree. E.g. rubber,
glass, cement
AS 6
Strain
Extension over original length (ratio). Stress is the cause & strain is the effect.
AS 6
Stress
It is the force per unit cross-section area required to stretch a material.
AS 6
Ultimate Tensile
Strength
The maximum force / original cross-sectional area the wire is able to support before it breaks
AS 6
Ultimate Tensile
Stress
The maximum value of stress that an object can sustain before it breaks.
AS 6
Young’s Modulus Ratio of stress to strain.
AS 7
Progressive
wave
The transfer or propagation of energy as a result of oscillations / vibrations
AS 7
Transverse
Waves
A wave in which displacement of particles is perpendicular to the direction of wave
propagation, resulting in crests & troughs. Transverse waves have vibrations that are
perpendicular / normal to the direction of energy travel
AS 7
Longitudinal
Waves
A wave in which displacement of particles is parallel to the direction of wave propagation.
Longitudinal waves have vibrations that are parallel to the direction of energy travel
AS 7
Wavelength
Distance moved by wave energy / wavefront during one cycle of the source or minimum
distance between two points with the same phase or between adjacent crests or troughs.
AS 7
Frequency (Hz)
Number of oscillations per unit time (not per second)
AS 7
Period
The time taken to complete one oscillation/cycle. Or time between adjacent wavefonts.
AS 7
Amplitude
Maximum displacement of a particle in the wave
AS 7
Displacement
Distance (of point on wave) from rest / equilibrium position
AS 7
Phase Difference
The difference in the relative positions of the crests or troughs of two waves of the same
frequency expressed in radians or degrees.
AS 7
(Wave) Intensity The intensity of a wave is the energy passing through unit area per unit time.
AS 7
(Wave) Speed
Speed at which energy is transferred / speed of wavefront. It is NOT the speed with which
particles in the wave move.
AS 7
Doppler Effect
Change in observed frequency when source moves relative to the observer
AS 7
electromagnetic waves (a transverse wave) can travel through a vacuum / free space. The
Electromagnetic
displacement in the case of electromagnetic waves is a variation in the electric & magnetic
Waves
fields perpendicular to each other.
AS 7
Polarisation
Oscillations or vibrations are in one direction, perpendicular to direction of propagation.
AS 8
Transfer of
Energy
The transfer of energy is due to a progressive wave, NOT a standing/stationary wave.
AS 8
Coherence
Two waves with a constant phase difference are said to be coherent.
AS 8
Principle of
Superposition
When two waves of the with similar frequency &amp meet/overlap, the resultant
displacement is the sum of the individual displacement of each wave.
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Cambridge A Level Physics: Definitions
AS 8
Node
Position along wave with no motion / zero amplitude
AS 8
Antinode
Position along wave with maximum amplitude.
AS 8
Constructive
Interference
Two waves' path difference is either λ or nλ, OR phase difference is 360°or n ×360° or n2π
AS 8
Destructive
Interference
Two waves' path difference is either λ/2 or (n+ ½) λ OR phase difference is odd multiple of
either 180° or π rad
AS 8
Two waves of same frequency/wavelength travelling (along the same line) in opposite
Stationary Waves directions overlap/meet. The resultant displacement is the sum of displacements of each
wave / produces nodes and antinodes
AS 8
Stationary Wave Does not transfer energy (no energy transfer). The amplitude of standing wave varies along
Properties
its length/nodes and antinodes.Neighboring points (in inter-nodal loop) vibrate in phase
AS 8
Fringe
The separation between one bright fringe & the next bright fringe.
Width/Separation
AS 8
Interference
When two waves superpose/overlap, the resultant displacement is the sum of individual
displacements of overlapping waves, forming alternating maxima and minima.
AS 8
Diffraction
When a wave (front) passes by/incident on an edge/slit, the wave spreads into the
geometrical shadow
AS 8
Diffraction
Grating
When waves pass through the gaps / slits in the grating, the wave bends/spreads (into the
geometrical shadow)
AS 8
Refraction
The change in direction of a wave due to change in speed.
AS 9
Ampere
If a charge of 1 Coulomb passes through an electrical component per second, then the
current maintained is 1 Ampere
AS 9
Charge
Charge = current x time
AS 9
Coulomb
The SI unit of electrical charge. A charge of 1C passes a point when a current of 1A flows for
1s.
AS 9
Electric Current
It is the amount of charge flowing pass a point per unit time.Or rate of flow of charged
particles.
AS 9
Ohm
volt/ampere
AS 9
Ohm’s Law
The current through a metallic conductor is proportional to the P.D across it provided that its
temperature remains constant.
AS 9
Potential
Difference
Energy converted from electrical to other forms of energy per unit charge that passes
through it.
AS 9
Quantised
Charge only exists in discrete amounts. Charge on carriers is quantised.
AS 9
Resistance
The ratio of P.D over the current for an electrical component
AS 9
Resistivity
The resistivity of a wire of a particular material is its resistance for unit length.
AS 9
Thermistor
A specific type of resistor, in which, as temperature increases, the magnitude of the resistor’s
resistance decreases, & vice versa.
AS 9
Volt
P.D between two points in a circuit in which 1J of energy is converted when 1C of charge
passes from one point to the other.
AS 10
E.m.f & P.D
While e.m.f refers to the amount of energy converted into electrical energy per unit charge
supplied, P.D refers to the amount of electrical energy converted into other forms of energy
per unit charge supplied. The e.m.f of a source is equal to the potential difference across its
terminals as the current approaches zero.
AS 10
Electromotive
Force
Energy converted from chemical into electrical energy per unit charge.
AS 10
Internal
Resistance
(resistance of the cell) causing loss of voltage or energy loss in cell
AS 10
Kirchhoff’s 1st
Law
The sum of currents into a junction = sum of currents out of junction, Because charge cannot
be created or destroyed (conservation of charge).
AS 10
Kirchhoff’s 2nd
Law
Sum of e.m.f.’s = sum of p.d.’s around a loop/circuit. Because any gains in electrical energy
of a charge must be balanced by corresponding losses of energy (conservation of energy).
AS 10
Law of
Conservation of
Charge
Kirchhoff’s First & Second Laws are in correspondence & actually are an appreciation of the
Law of Conservation of Charge & the Law of Conservation of Energy respectively.
10
Output Power
(Circuit)
A battery delivers the maximum power to a circuit when the load resistance of the circuit is
equal to the internal resistance of the battery. When load resistance is zero, power
dissipated by load is zero because P=I^2R. When load resistance is very large, power
dissipated gets very small as the current through the load is reduced significantly.
AS 10
Potentiometer
When a potential divider arrangement is used to compare e.m.fs of two sources, it is known
a potentiometer.
AS 11
Alpha particle
Either helium nucleus OR particle containing two protons and two neutrons with mass 4u.
Radiation can be deflected in electric/magnetic fields, and absorbed by thin paper or few cm
of air. Radiation is highly ionizing.
Baryon
A type of hadron particle that is made up of three quarks (e.g. proton and neutron).
AS 11
Beta Particle
Produced due to weak nuclear force/interaction. β-particles are fast moving electrons with a
range of speeds up to 0.99c. This radiation can be deflected by electric and magnetic fields
or negatively charged, and absorbed by few (1 – 4) mm of aluminum. 0.5 to 2m for range in
air.
AS 11
Gamma
Radiation
γ- radiation is part of the electromagnetic spectrum with wavelengths between 10^(-11) m
and 10^(-13) m.
Hadron
Class of heavy particles made up of quarks held together by strong nuclear force. Hadron is
not a fundamental particle.
Isotopes
Atoms (same element) which have the same proton number, but a different nucleon number
/ number of neutrons.
Meson
A type of hadron particle that is made up of two quarks.
11
11
AS 11
11
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Cambridge A Level Physics: Definitions
AS 11
Nucleon (mass)
Number
The number of protons together with the number of neutrons in the nucleus is called the
nucleon number (or mass number) A
AS 11
Proton Number
The number of protons in the nucleus of an atom ( aka atomic number) Z
The Atom
The simple model of the atom is made up of three sub-atomic particles: The proton (which is
positively charged), the neutron (which is uncharged but equal in mass to the proton), & the
electron (which is negatively charged & equal to the charge on the proton, but much smaller
in size & mass).
AS 11
Jump to sections:
[AS Chapters][A2 Chapters]
===================
A2 Level Physics Terms & Concepts
Useful set of flashcards for A2 revision
https://quizlet.com/392317817/cie-physics-a-level-definitions-flash-cards/
Lvl Ch
Term
Definition
A2 12
Angular
displacement
the angle through which the object has moved
A2 12
Radian
angle subtended at the centre of a circle by an arc of length equal to the radius of the circle
A2 12
Angular velocity
rate of change of angular displacement
A2 12
Angular
acceleration
rate of change of angular velocity
A2 13
Newton’s Law of any two point masses attract each other a force that is directly proportional to the product of
Gravitation
their masses and inversely proportional to the square of the separation
A2 13
Gravitational field
gravitational force exerted per unit mass on a small object placed at that point
strength, g
A2 13
Field of force
A region of space where a force acts (on a particle of certain property)
A2 13
Gravitational
potential
work done per unit mass in bringing unit mass from infinity to the point
A2 13
Geostationary
orbits
Orbit in which a satellite is positioned so that it orbits the Earth the same rate as the Earth’s
rotation. Satellite remains above a fixed point on the Earth’s surface
A2 15
Mole
amount of that substance which contains the same number of particles as there are in 0.012
kg of carbon-12
A2 15
Avogadro's
constant
amoung of carbon-12 atoms in 12g of Carbon-12
A2 15
Boyle’s law
pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the
temperature of gas remains constant
A2 15
Charles’ Law
temperature acting on a fixed mass of gas is directly proportional to its volume, provided the
pressure of gas remains constant
A2 15
Ideal gas
Gas that behaves and obeys all law
A2 14
Thermal
Equilibrium
a condition when two or more objects in contact have the same temperature so that there is
no net flow of thermal energy
A2 14
Thermocouple
device consisting of wires of two different metals across which an emf is produced when the
two junctions of the wires are at different temperature
A2 14
Temperature
Amount of average kinetic energy of particles, and shows direction of net heat flow between
two bodies in contact.
A2 14
Fixed points
Standard reference temperatures that are used when calibrating thermometers.
A2 14
Absolute zero
Temperature at which atoms have minimum or zero energy.
A2 14
Calibration
Uses fixed points as upper/lower points and assumes a linear change of property with
temperature.
A2 14
Thermodynamic /
Scale does not depend on the property of a substance
Absolute Scale
A2 16
Internal energy
A2 16
First Law of
the increase in internal energy of a body is equal to the thermal energy transferred to it by
Thermodynamics heating plus the mechanical work done on it
A2 14
Heat / Thermal
Energy
energy transferred from one object to another because of temperature difference. Increases
internal energy.
A2 14
Specific heat
capacity
energy required per unit mass of the substance per unit °C to raise the temperature by 1 K
or 1°C.
A2 14
Specific latent
heat
energy required per kilogram of the substance to change its state without any change in
temperature
A2 14
Specific latent
heat of fusion
energy required per kilogram of a substance to change it from solid to liquid without a
change in temperature
A2 14
Specific latent
heat of
vaporisation
energy required per kilogram of a substance to change it from liquid to gas without a change
in temperature
A2 14
Boiling
The process by which a liquid changes into its gaseous state at a constant specific
temperature, known as boiling point. Heat energy goes towards overcoming intermolecular
forces to move the atoms far enough so that interatomic forces and potential energy are
negligible.
A2 16
Brownian Motion
The haphazard or random movement of tiny suspended particles (such as smoke, pollen
etc.) in a fluid is known as Brownian Motion.
sum of the random distribution of kinetic and potential energies of its atoms or molecules
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