Definitions and Concepts For CAIE Physics GCSE

Definitions and Concepts for CAIE Physics GCSE
Topic 1: General Physics
Definitions in bold are for extended students only
1.1 Length and Time
Analogue device: A measuring device that requires the user to read from a scale
to obtain the measurement.
Digital device: A measuring device that displays the measurement on a display,

rather than requiring the user to read from a scale.
Distance: A measure of how far an object moves. It doesn’t depend on direction

and is therefore a scalar quantity.
Micrometer screw gauge: A measuring implement used to accurately

measure very small distances.
Pendulum: A pendulum is a weight suspended from a pivot so that it can swing

freely.
Volume: The amount of space that a substance or object occupies.
1.2 Motion
Acceleration: The rate of change of velocity. It can be calculated from the

gradient of a velocity-time graph. Denoted by non-zero gradient in a speed-time
graph.
Air resistance: The resistance of an object’s motion through air. It is a form

of friction due to the air particles colliding with the object.
Average speed: The average speed is calculated by dividing the distance

travelled by the time taken.
Deceleration: Negative acceleration.
Distance–time graph: A plot of how an object’s distance changes over time. The
gradient of the graph at any point, equals the object’s speed at that point.
Free fall: Motion under the force of gravity alone.
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Linear motion: Motion for which the acceleration is not constant.
Speed: A scalar quantity that is a measure of the rate of change of distance.
Speed–time graph: A plot of how an object’s speed changes over time. The
gradient of the graph at any point, equals the object’s acceleration at that
point. The area under the graph represents the distance travelled.
Terminal velocity: Steady speed achieved by an object freely falling through

a gas or liquid.
Gravitational field: A region where a mass will experience a non-contact

gravitational force. All matter produces a gravitational field around it, and
the greater its mass, the stronger the field.
Velocity: A vector quantity that is a measure of the rate of change of

displacement. It is the speed in a given direction.
1.3 Mass and Weight
Balance: A piece of apparatus that can compare different weights to demonstrate

which is greater. It can also be used to compare masses.
Mass: Mass is a measurement of how much matter is in an object. It is also the
resistance that a body offers to a change in its speed or position upon the
application of a force.
Weight: The force acting on an object due to gravity. It is equal to the product of
the object’s mass and the gravitational field strength at its location.
1.4 Density
Density: The mass per unit volume of an object.
Displacement: It is the object's overall change in position. Calculated by the

difference between final and initial readings.
1.5 Forces
1.5.1 Effects of Forces
Air resistance: The resistance of an object’s motion through air. It is a form of

friction due to the air particles colliding with the object.
Extension–load graphs: A graph that shows how the extension of an object

varies with the load applied. For a spring, this should initially form a straight line
that passes through the origin.
Friction: A resistive contact force that acts to oppose the relative motion between
two surfaces. Some energy of the object in contact is lost as heat in the process.
Hooke’s law : The extension of a spring is directly proportional to the force

applied to it, up to the limit of proportionality. The constant in this
relationship is known as the spring constant.
Limit of proportionality: The point beyond which the extension of an elastic

object is no longer directly proportional to the force applied to it.
Resultant force: The single force that can replace all the individual forces acting
on an object, and have the same effect.
Spring constant: A measure of a spring’s stiffness. The higher the spring

constant, the smaller the extension is for a given force.
1.5.2 Turning Effect
Moment of a force: The turning effect of a force, equal to the product of the
magnitude of the force and the perpendicular distance from the pivot to the line of
action of the force.
Principle of moments: For an object in equilibrium, the sum of the clockwise

moments about any point on the object must equal the anticlockwise moments
about that same point.
1.5.3 Conditions for Equilibrium
Equilibrium: An object in equilibrium has a zero resultant force and a zero
resultant moment.
Resultant force: The single force that can replace all the individual forces acting
on an object, and have the same effect.
Turning effect: It is also known as the moment of the force.
1.5.4 Centre of Mass
Centre of mass: The single point through which all the mass of an object can be
said to act.
Plane lamina: A body whose mass is concentrated in a single plane.
Stability: A measure of the likelihood of an object toppling. An object is unstable if

the object’s line of action of weight lies outside of its base.
1.5.5 Scalars and Vectors
Resultant vector: It is the sum of two or more vectors which has its own
magnitude and direction
Scalars: Quantities that only have a magnitude, not a direction.
Vectors: Quantities that have both a magnitude and direction. They are
represented by an arrow, with the length representing the magnitude and the
arrowhead representing the direction.
1.6 Momentum
Conservation of momentum: The total momentum of a system before an

event is always equal to the total momentum of the system after the event.
Impulse: The change of a system’s momentum as a result of a force acting

over a period of time
Momentum: The product of an object’s mass and velocity.
1.7 Energy, Work and Power
1.7.1 Energy
Chemical energy: A store of energy found in things such as batteries, fuels and
food.
Elastic potential (strain) energy: The store of energy that stretched or

compressed objects contain.
Electrical current: An electric current is a flow of electric charge in a circuit.
Gravitational potential energy: The store of energy that all raised matter has. It
is directly proportional to the mass of the object, the distance that it is
raised, and the gravitational field strength at that point.
Internal energy: It is defined as the energy associated with the random,
disordered motion of molecules.
Kinetic energy: The store of energy that all moving matter has. It is directly
proportional to the object’s mass and to the square of its velocity.
Nuclear energy: Non-renewable energy that is generated from the energy stored
in the nuclei of radioactive isotopes. It is released in processes known as nuclear
fission and nuclear fusion.
Principle of conservation of energy: The law that energy can be transferred,
stored or dissipated but never created or destroyed.
1.7.2 Energy Resources
Chemical energy: A store of energy found in things such as batteries, fuels and
food.
Efficiency: The ratio of useful output energy transfer to total energy input. It can
never exceed 1 (or 100%), due to the conservation of energy.
Geothermal energy: Renewable energy generated from the conversion of the

thermal energy found below the Earth’s surface into electrical energy.
Hydroelectric power: Renewable energy generated by water stored at a height,

and released through a turbine. The turbine turns a generator which converts the
kinetic energy into electrical energy.
Nuclear fission: It is a process where the nucleus of an atom is split into two or
more smaller nuclei.
Nuclear fusion: It is the process of making a single heavy nucleus (part of an
atom) from two lighter nuclei.
Renewable energy resource: An energy resource that can be replenished whilst
it is being used.
Solar energy: Renewable energy generated by converting the energy of the sun
into electrical energy, usually by using a solar panel.
Tidal energy: Renewable energy generated by trapping water when at high tide,
and then releasing it through a turbine. The turbine turns a generator which
converts the kinetic energy into electrical energy.
Wind energy: Refers to the process of creating electricity using the wind.
1.7.3 Work
Work done: Work is done on an object when a force causes it to move through a
distance. It is equal to the product of the distance travelled and the magnitude of
the force in the direction of motion.
1.7.4 Power
Power: The rate at which energy is transferred, or the rate at which work is done.
It is calculated by dividing the work done by the time taken.
Work done: Work is done on an object when a force causes it to move through a
distance. It is equal to the product of the distance travelled and the magnitude of
the force in the direction of motion.
1.8 Pressure
Atmosphere: The thin layer of air surrounding the Earth, which gets less dense
with increasing altitude. The pressure also decreases with increasing altitude.
Atmospheric pressure: It is the force exerted on a surface by the air above it as
gravity pulls it to Earth
Manometer: A U-shaped tube of liquid that allows the pressure on a column of

liquid to be measured.
Mercury barometer: A measuring device that measures changes in atmospheric

pressure.
Pressure: The force acting perpendicular to a surface, per unit area.
Topic 2: Thermal Physics
2.1 Simple Kinetic Molecular Model of Matter
2.1.1 States of Matter
Gases: A state of matter in which the particles are spread apart and have
high kinetic energies. Any intermolecular forces acting between the particles
are very weak.
Liquids: A state of matter in which the particles are in contact, but can flow
over each other. Intermolecular forces act between the particles.
Solids: A state of matter in which the particles are tightly packed together
and can only vibrate about their fixed positions. Strong intermolecular
forces act between the particles.
2.1.2 Molecular Model
Brownian motion: It is the random motion of particles suspended in a medium
Gas temperature: The temperature of a gas is directly proportional to the average

kinetic energy of its molecules.
Kinetic molecular model of matter: States that matter is made up of particles

that are constantly moving.
Pressure of a gas: The perpendicular force(rate of change of momentum) per

unit area acting on the surfaces of a container as a result of the gas particles
colliding with it.
Suspension: A state in which particles are dispersed throughout a fluid.
2.1.3 Evaporation
Evaporation: It is the process of changing from a liquid or solid state into vapor
due to the escape of more-energetic molecules from the surface of a liquid. It is
influenced by temperature, surface area and draught over a surface.
Evaporative cooling: It is cooling due to evaporation due to the escape of

more-energetic molecules from the surface of a liquid. As a result, a body in
contact with an evaporating liquid also experiences a loss in temperature.
2.1.4 Pressure Changes
Molecule: It is a particle made up of two or more atoms that are chemically

bonded together.
Temperature: A measure of the average kinetic energy of the particles in a

substance. An increase in temperature will result in an increase in the particles’
kinetic energies and velocities.
Volume of a gas: It is the quantity of three-dimensional space occupied by a gas.
2.2 Thermal Properties and Temperature
2.2.1 Thermal Expansion of Solids, Liquids and Gases
Application: The action of putting something into operation.
Magnitude: A numerical quantity or value.
Thermal expansion: Thermal expansion is the increase, or decrease, of the size

(length, area, or volume) of a body due to a change in temperature.
2.2.2 Measurement of Temperature
Fixed points: A well-defined reproducible temperature which can be used as a

reference point.
Liquid-in-glass thermometer: An instrument for measuring and indicating

temperature in which the thermally sensitive element is a liquid contained in a
graduated glass envelope, which uses the thermal expansion of the liquid to
measure readings.
Linearity of a thermometer: It is the property in a thermometer defined as the

same distance between all degree intervals.
Measurement: It is the process of associating numbers with physical quantities.
Physical property: is any property that is measurable, whose value describes a
state of a physical system.
Range of a thermometer: It is the difference between the maximum and

minimum temperatures that the thermometer can read.
Sensitivity of a thermometer: It is defined as the increase in the length of the

mercury column per unit increase in temperature.
Thermocouple: A device for measuring temperature in which a pair of wires
of dissimilar metals (such as copper and iron) are joined and the free ends
of the wires are connected to an instrument (such as a voltmeter) that
measures the difference in potential created at the junction of the two
metals.
2.2.3 Thermal Capacity (Heat Capacity)
Change in Thermal Energy: The product of the mass, specific heat capacity
and temperature change of a substance.
Internal energy: The energy stored by the atoms and molecules that make up a
system. It is equal to the sum of the total kinetic and potential energies of the
particles in the system.
Specific heat capacity: The amount of energy needed to increase the

temperature of one kilogram of a given substance by one degree Celsius.
Thermal capacity: It is defined as the amount of heat to be supplied to a given

mass of a material to produce a unit change in its temperature.
2.2.4 Melting and Boiling
Boiling: It is the physical process that results in the transition of a substance from
a liquid to a gas state without change in temperature.
Boiling point: It is the temperature at which a substance changes state from a
liquid to a gas.
Condensation: The changing from vapour state to a liquid state, when a

substance is cooled. As the molecules lose heat, they lose energy and slow down.
Evaporation: Is the process by which an element or compound transitions

from its liquid state to its gaseous state below the temperature at which it
boils.
Latent heat: The energy required for a substance to change state.
Melting: It is the physical process that results in the transition of a substance from
a solid to a liquid state without change in temperature.
Melting point: It is the temperature at which a substance changes state from solid
to liquid.
Solidification: It is a phase transition in which a liquid turns into a solid when its
temperature is lowered to or below its freezing point. As the molecules lose heat,
they lose their kinetic energy and band together.
Specific latent heat of vaporisation: The amount of energy needed to change
the state of one kilogram of a substance from liquid state to vapour state,
whilst held at constant temperature.
Specific latent heat of fusion: The amount of energy needed to change the
state of one kilogram of a substance from solid state to liquid state, whilst
held at constant temperature.
Specific latent heat: The amount of energy needed to change the state of
one kilogram of a substance, whilst held at constant temperature.
2.3 Thermal Processes
2.3.1 Conduction
Conduction: The transfer of heat energy through the vibrations of particles in a

medium.
Electron: A stable subatomic particle with a charge of negative electricity,

found in all atoms
Lattice Vibration: is the oscillations of atoms in a solid about the equilibrium
position
Thermal conductor: It is a material that allows energy in the form of heat, to be

transferred within the material, without any movement of the material itself.
2.3.2 Convection
Convection: The transfer of heat energy through convection currents in a fluid.
Density: It is a property of the substance, also known as mass per unit volume.
2.3.3 Radiation
Absorption: The transfer of the energy of a wave to matter as the wave passes
through it.
Electromagnetic spectrum: A group of transverse waves that cover a large

range of frequencies and wavelengths. The highest frequency waves in the
spectrum are gamma-rays and the lowest are radio waves.
Infrared radiation: A type of radiation that all objects emit and absorb. The hotter
an object is, the greater the infrared radiation it emits in a given time.
Medium: Is defined as the substance that transfers energy from one substance to
another substance.
Reflection: The bouncing back of a wave at a boundary.
Thermal energy: The store of energy that all objects with a temperature contain.
The higher the temperature, the greater its thermal energy store.
2.3.4 Consequences of Energy Transfer
Conduction: The transfer of heat energy through the vibrations of particles in a

medium.
Convection: The transfer of heat energy through convection currents in a fluid.
Radiation: The emission of energy as electromagnetic waves or as moving

subatomic particles.
Topic 3: Properties of Waves, Including Light

and Sound
3.1 General Wave Properties
Amplitude: The maximum displacement of a wave from its undisturbed (equilibrium)

position.
Diffraction: It is the bending of waves around gaps or corners. It occurs when the size of
the aperture or obstacle is of the same order of magnitude as the wavelength of the
incident wave.
Frequency: The number of waves passing a given point in a second. It is the inverse of the
wave’s time period.
Longitudinal waves: Waves with oscillations that are parallel to the direction of
travel/energy transfer.
Reflection: The bouncing back of a wave at a boundary.
Refraction: The changing of speed, and consequently the direction, of a wave as it changes
medium. The wavelength of the wave will also change but the frequency remains constant.
Speed of a wave: The speed is the distance traveled by a given point on the wave in a given
interval of time.
Transverse waves: Waves with oscillations that are perpendicular to the direction of
travel/energy transfer.
Vibration: Is a mechanical phenomenon whereby oscillations occur about an equilibrium

point.
Water waves: They are waves propagating on the water surface.
Wave: A process of energy transfer through oscillations, without matter being transferred
with it.
Wavefront: An imaginary surface representing points of a wave that are at the same point in
their cycle.

Wavelength: The distance from a point on one wave to the same point on the adjacent wave
(ie. peak to peak or trough to trough).
3.2 Light
3.2.1 Reflection of Light
Angle of incidence: The angle which an incident line or ray makes with a perpendicular to
the surface at the point of incidence.
Angle of reflection: The angle made by a reflected ray with a perpendicular to the reflecting
surface.
Optical image: It is the apparent reproduction of an object, formed by a lens or mirror
system from reflected, refracted, or diffracted light waves.
Plane mirror: It is a flat reflective surface. The image formed by a plane mirror is always
virtual, upright, and of the same shape and size as the object it is reflecting.
3.2.2 Refraction of Light
Critical angle: The angle of incidence beyond which all the wave is totally internally reflected
when it meets a boundary.
Optical fibres: A thin flexible fibre with a glass core through which light signals can be
transmitted along its axis, by the process of total internal reflection.
Parallel: Two lines that are always the same distance apart and never meet.
Refractive Index: The ratio of the speed of the wave in a vacuum to the speed of the
wave in a given medium.
Transparent: A material allowing light to pass through.
Total internal reflection: The process of all a wave being reflected when it meets a
boundary. It occurs when the angle of incidence is greater than the critical angle, and only
when going from a higher refractive index to a lower one.
3.2.3 Thin Converging Lens
Diminished: Made smaller or less.
Enlarged: Having become or been made larger.
Focal length: Is the distance between the centre of the lens and the principal focus.
Focus: Is the point where light rays originating from a point on the object converge.
Magnifying glass: It is a convex lens that lets the observer see a larger image of the
object under observation.
Principal focus: Is the point where rays of light travelling parallel to the principal axis
intersect the principal axis and converge.
Real Image: An image produced by light-rays physically converging. Real images are ones
that can be projected onto a screen.
Single lens: A lens that consists of a single piece of transparent material.
Thin converging lens: Lens that focuses the diverging, or blurred, light rays from a distant
object by refracting (bending) the rays.
Virtual image: An image produced by the apparent, but not actual, divergence of
light-rays. Virtual images cannot be projected onto a screen.
3.2.4 Dispersion of Light
Dispersion: Is defined to be the spreading of white light into its full spectrum of wavelengths.
Glass prism: Is a transparent optical element with flat, polished surfaces that refract light.
Monochromatic light: Is light where the optical spectrum contains only a single optical
frequency.
Spectrum: Is the range of frequencies of electromagnetic radiation and their respective
wavelengths and photon energies.
3.3 Electromagnetic Spectrum
Electromagnetic spectrum: A group of transverse waves that cover a large range of

frequencies and wavelengths. The highest frequency waves in the spectrum are gamma-rays
and the lowest are radio waves. Speed of electromagnetic waves in a vacuum is 3.0 × 108
m/s and is approximately the same in air.
Infrared: Used for cooking food, thermal imaging and short range communications. It can
cause skin burns.
Microwaves: Used for satellite communications and for cooking food. They can cause
internal heating of body cells.
Radio Waves: Used for television and radio signals. They can be produced by
oscillations in electrical circuits, or can induce these oscillations themselves.
Vacuum: Space in which there is no matter
Wavelength: The distance from a point on one wave to the same point on the adjacent wave
(ie. peak to peak or trough to trough).
X-Rays: Used for medical imaging and security scanners. They can cause cell damage and
mutations.
3.4 Sound
Audible frequencies: It is a periodic vibration whose frequency is in the band audible to the
average human, the human hearing range, which is 20Hz to 20000Hz
Compressions: They are regions of high pressure due to particles being close together.
Echo: Is a distinct, reflected sound wave from a surface.
Loudness: A measure of the amplitude of the oscillations of a sound wave. The larger the
amplitude, the louder the sound will be.
Pitch: A measure of the frequency of the oscillations of a sound wave. The higher the
frequency, the higher the pitch of the sound.
Rarefactions: They are regions of low pressure due to particles being spread further apart.
Sound waves: The longitudinal waves responsible for sound. They are produced by
vibrating sources and they require a medium to travel through, transmitted by the vibrations
of the medium’s particles.
Speed of sound: The speed of sound is the distance travelled per unit of time by a sound
wave as it propagates through a medium.
Ultrasound waves: Waves that have a frequency higher than the upper limit of human
hearing (20kHz).
Topic 4: Electricity and Magnetism
4.1 Simple Phenomena of Magnetism
Alternating current: Current flow consisting of charges that continually change

direction. These oscillations usually occur at a set frequency.
Bar magnet: Is a rectangular piece of an object that shows permanent magnetic

properties.
Demagnetisation: Process of removing magnetic qualities in a material.
Direct current: Current flow consisting of charges flowing in a single direction

only. Batteries and cells provide direct current.
Electromagnet: A solenoid with an iron core. The magnetism of an electromagnet can

be switched on and off, and the strength changed, through varying the current in the
solenoid.
Induced magnet: A material that becomes a magnet when it is placed in an

existing magnetic field, but loses its magnetism quickly once it is removed.
Induced magnetism always produces attractive forces.
Magnet : A magnet is a material or object that produces a magnetic field.
Magnetisation: Process of inducing magnetic qualities in a material.
Magnetic field: The region around a magnet in which another magnet or

magnetic material will experience a force.
Magnetic field lines: Lines that show the strength and direction of a magnetic field.
The lines point from North to South and their concentration represents the magnitude
of the field
Magnetic materials: Iron, steel, cobalt and nickel.
Non-magnetic materials: Materials which are not attracted by a magnet.
Permanent magnet: A magnet that produces its own magnetic field.

4.2 Electrical Quantities
4.2.1 Electric Charge
Charging by induction: Is a method used to charge an object without actually

touching the object to any other charged object.
Conductor: A material that allows electrical charge to flow easily. Metals are
particularly good conductors due to the free electrons in their structures.
Coulomb: The unit of charge.
Electric charge: Is the physical property of matter that causes it to experience a

force when placed in an electromagnetic field. There are two types of electric
charges: positive and negative.
Electric field: A region in which a charge will experience a non-contact,

electric force. All charged objects have an electric field around them, and
this field is stronger the closer you are to the charge.
Electrostatic charge - The electric charge at rest on the surface of an insulated body.
Insulator: A material that doesn’t allow electrical charge to flow.
Like charges: When two charges of the same polarity meet, they will repel.
Point charge: The electric field around a point charge becomes weaker the
further away you are. The field lines for a positive charge point radially
outwards, whereas the field lines for a negative charge point radially
inwards.
Unlike charges: When two charges of opposite polarities meet, they will attract.
4.2.2 Current
Ammeter: A device connected in series with a component to measure the current that
flows through it
Analogue device: A measuring device that requires the user to read from a scale
to obtain the measurement.
Conventional current: Is defined as moving in the same direction as the

positive charge flow.
Digital device: A measuring device that displays the measurement on a display, rather
than requiring the user to read from a scale..
Electric Current: The rate of flow of electrical charge. Its value is the same at any
position in a single closed loop. In metals, the charges that flow are electrons.
4.2.3 Electromotive Force
Electromotive force: The energy supplied by a source in driving charge

round a complete circuit. Measured in Volts.
Volt: The unit of potential difference (voltage). One volt is equal to one joule per
coulomb.
4.2.4 Potential Difference
Potential difference: The energy that is transferred per unit charge between
two points in a circuit. It is often also called a voltage and measured in volts.
Voltmeter: A device that is connected in parallel with a component to measure the

potential difference (voltage) across it.
4.2.5 Resistance
Ammeter: A device connected in series with a component to measure the current that
flows through it.
Current–voltage characteristic: Is a relationship, typically represented as a chart

or graph, between the electric current through a circuit and the corresponding
voltage, or potential difference across it.
Filament lamp: A light emitting component consisting of an enclosed metal

filament. Its resistance increases as the filament’s temperature increases.
Ohmic resistor: A resistor that functions according to Ohm's law.
Resistance: A measure of the opposition to current flow. Calculated as ratio of the p.d.
applied to the electric current which flows through it:
4.2.6 Electrical Working
Battery: Is a device that stores chemical energy and converts it to electrical

energy.
Power: The rate at which an appliance transfers energy. For a circuit component, it
is equal to the product of the current passing through it and the potential
difference across it.
4.3 Electric Circuits
4.3.1 Circuit Diagrams
Circuit diagram: Is a graphical representation of an electrical circuit.
Diode: A component that only allows current to flow through in the forward
direction. They have very large resistances in the reverse direction.
Electric heater: Is an electrical device that converts an electric current into heat.
Filament lamp: A light emitting component consisting of an enclosed metal filament.

Its resistance increases as the filament’s temperature increases.
Fixed resistors: Are the resistors whose resistance does not change with the
change in voltage or temperature.
Fuse: A safety device consisting of a thin metal filament that melts and cuts off the
power supply if there is a surge in current. Fuses are connected to the live wire.
Galvanometer: Is an electromechanical instrument used for detecting and

indicating an electric current.
Light dependent resistor (LDR): A light sensitive component whose resistance

decreases as its temperature increases.
Relay: Is a special type of switch turned on and off by an electromagnet.
Switch: Is a device used for making and breaking electric current through the
circuit.
Thermistor: A temperature dependent component, whose resistance increases

as its temperature decreases.
Transformer: An iron core with a primary and secondary coil of wire wound around
opposite ends. Transformers can change the magnitude of an alternating voltage.
Variable resistor: Is a resistor of which the electric resistance value can be

adjusted.
4.3.2 Series and Parallel Circuits
Parallel: Components connected in parallel have the same potential difference

across each component. The current from the source is larger than the current in
each branch and the total current is equal to the sum of the currents flowing
through each component.
Resistors in parallel: The total resistance is less than the lowest individual
resistance.
Resistors in series: The total resistance is equal to the sum of the resistances of
the individual resistors.
Series: Components connected in series have the same current passing through
each component but share the total potential difference (voltage) of the power
supply. The sum of the potential difference across the components in a
series circuit is equal to the total potential difference across the supply.
4.3.3 Action and use of Circuit Components
Input transducers: Is a device that takes a form of physical energy and converts
it into a signal which can be read.
Light dependent resistor (LDR): A light sensitive component whose resistance

decreases as its temperature increases.
Rectifier: Is an electrical device that converts alternating current (AC) to

direct current (DC).
Switch: Is a device used for making and breaking electric current through the circuit.
Thermistor: A temperature dependent component, whose resistance increases as its

temperature decreases.
Variable potential divider: Is a simple circuit that uses resistors(or thermistors /

LDRs) to supply a variable potential difference.
4.4 Digital Electronics
Analogue: They are electronic systems with a continuously variable signal.
AND gate: Is a logic gate that implements logical conjunction.
Digital: A waveform that switches representing the two states of low and
high.
NAND gate: Is a logical gate which is the opposite of an AND logic gate.
NOR gate: Is a logical gate which is the opposite of an OR logic gate.
NOT gate: Is a logic gate which implements logical negation.
OR gate: Is a logic gate that implements logical disjunction.
Truth table: Is a mathematical table used in logic which sets out the
functional values of logical expressions on each of their functional
arguments.
4.5 Dangers of Electricity
Circuit breaker: A safety device that cuts off the power supply if a surge of current
passes through it. Circuit breakers can be reset and are quicker acting than fuses.
Earthing: The removal of excess charge by providing a low resistance path for
electrons to flow through.
Fuse: A safety device consisting of a thin metal filament that melts and cuts off the
power supply if there is a surge in current. Fuses are connected to the live wire.
Insulator: A material that doesn’t allow electrical charge to flow.
4.6 Electromagnetic Effects
4.6.1 Electromagnetic Induction
Electromagnetic induction: Is the production of an electromotive force across an

electrical conductor in a changing magnetic field. The direction of an induced e.m.f.
opposes the change causing it
Induced current: The current induced in a conducting loop that is exposed to a

changing magnetic field
Magnetic field: The region around a magnet in which another magnet or magnetic
material will experience a non-contact force.
4.6.2 a.c. Generator
Alternating current: Current flow consisting of charges that continually change

direction. These oscillations usually occur at a set frequency.
Direct current: Current flow consisting of charges flowing in a single direction only.
Batteries and cells provide direct current.
Generator effect: When there is relative motion between an electrical

conductor and a magnetic field, a potential difference will be induced across
the ends of the conductor. A current will flow if this conductor is part of a
complete circuit.
Rotating-coil generator: A device consisting of a coil, which when spun in a

magnetic field, induces a current in the coil.
Slip ring: Is an electromechanical device that allows the transmission of

power and electrical signals from a stationary to a rotating structure.
4.6.3 Transformer
High-voltage transmission: Electricity is transported along them at very high voltages

to reduce the energy loss and make the transportation more efficient.
Step-Down transformer: A transformer that has a smaller potential difference in the

secondary coil than in the primary coil. This is a result of the secondary coil having
fewer turns.
Step-Up transformer: A transformer that has a larger potential difference in the

secondary coil than in the primary coil. This is a result of the secondary coil having
more turns.
Transformer: An iron core with a primary and secondary coil of wire wound around
opposite ends. Transformers can change the magnitude of an alternating voltage.
Turns ratio: The number of turns in the primary coil of a transformer over the number
of turns in the secondary coil. This is equal to the voltage ratio for a 100% efficient
transformer.
Voltage ratio: The voltage across the primary coil of a transformer over the voltage
across the secondary coil.
4.6.4 The Magnetic Effect of a Current
Magnetic field: The region around a magnet in which another magnet or magnetic
material will experience a non-contact force. The direction of a magnetic field line at
a point is the direction of the force on the N pole of a magnet at that point.
Solenoid: A wire wrapped into the shape of a coil, that has a strong and uniform
magnetic field inside of it. The solenoid’s magnetic field strength can be increased by
adding an iron core.
4.6.5 Force on a Current-Carrying Conductor
Beam of charged particles: Is a spatially localized group of electrically

charged particles that have approximately the same position, kinetic energy,
and direction.
Charged particle: Is a particle with an electric charge.
4.6.6 d.c. Motor
Electric motor: A current-carrying coil of wire in a magnetic field. The two sides of the
coil that are perpendicular to the magnetic field experience forces in opposite
directions, causing rotation.The effect is increased by increasing the number of turns
on the coil, increasing the current, or increasing the strength of the magnetic field
Split-ring commutator: Device used to reverse the direction of the current in

the coil each half turn. This allows the motor coil to rotate continuously in
one direction.
Topic 5: Atomic Physics
5.1 The Nuclear Atom
5.1.1 Atomic Model
Alpha particle: A positively charged particle consisting of two protons and two
neutrons. They are highly ionising, but can be stopped by a few centimetres of
air.
Atom: The smallest component of an element having the chemical properties of

the element, consisting of a nucleus containing combinations of neutrons and
protons and one or more electrons bound to the nucleus by electrical attraction.
Electrons: A negatively charged constituent of the atom, that are found in different
energy levels, around the nucleus.
5.1.2 Nucleus
Isotopes: Atoms with the same number of protons but different numbers of neutrons.
The atomic number is the same, but the mass number is different.
Nuclear fission: The splitting of a large and unstable nucleus into two smaller
and more stable nuclei to produce energy. This is the method currently used in
nuclear power stations.
Nuclear fusion: The joining of two small, light nuclei to form a larger, heavier
one and release energy. It cannot happen at low pressures and temperatures
since in these conditions the electrostatic repulsion of protons in the
nucleus cannot be overcome.
Nucleon number: The number of protons and neutrons in an atom.
Nucleus: Is a collection of particles called protons, which are positively charged,
and neutrons, which are electrically neutral.
Nuclide: Refers to an atom with a distinct number of protons and neutrons in its
nucleus.
Nuclide notation: Is a shorthand method of showing information about atoms.

Proton number: The number of protons found in an atom of a specific element. Each
element has a different proton number.
5.2 Radioactivity
5.2.1 Detection of Radioactivity
Background radiation: Radiation that is found in small quantities all around us and
originates from natural sources such as rocks and cosmic rays, as well as from
man-made sources such as nuclear weapons testing and accidents.
Beta particle: A high speed electron that a nucleus emits when a neutron converts
into a proton. They are ionising but can be stopped by a thin sheet of aluminium.
Gamma ray: Electromagnetic radiation emitted from a nucleus. They have a very high
penetrating power and require several centimetre of lead to absorb them.
5.2.2 Characteristics of the three kinds of Emission
Ionisation: The process in which an electron is given enough energy to

break away from an atom.
Random nature of radioactive decay: You cannot predict which nuclei in a

radioactive sample will decay next, or when the next decay will occur - it is a random
process.
5.2.3 Radioactive Decay
Radioactive decay: The random process involving unstable nuclei emitting radiation
to become more stable. During α- or β-decay the nucleus changes to that of a different
element.
5.2.4 Half-Life
Half life: The time it takes for the number of unstable nuclei of an isotope in a
sample to halve, or the time it takes for the initial count rate of a sample of the
isotope to halve. It is different for different isotopes.
5.2.5 Safety Precautions
Ionising radiation: Radiation that can cause cell mutations, damage cells and tissues,
and lead to cancers.

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Definitions and Concepts for CAIE Physics GCSE

Topic 1: General Physics

Definitions in ​bold ​are for extended students only

1.1 Length and Time

Digital device​:​ A measuring device that displays the measurement on a display,

Distance: ​A measure of how far an object moves. It doesn’t depend on direction

Micrometer screw gauge​:​ ​A measuring implement used to accurately

Pendulum​:​ A pendulum is a weight suspended from a pivot so that it can swing

Volume​:​ ​The amount of space that a substance or object occupies.

Acceleration​:​ ​The rate of change of velocity. It can be calculated from the

Air resistance​: The resistance of an object’s motion through air. It is a form

Average speed​: ​The average speed is calculated by dividing the distance

Deceleration​: Negative acceleration.

Free fall​: ​Motion under the force of gravity alone.

This work by PMT Education is licensed under https://bit.ly/pmt-cc

Speed​: ​A scalar quantity that is a measure of the rate of change of distance.

Terminal velocity​: Steady speed achieved by an object freely falling through

Gravitational field​: A region where a mass will experience a non-contact

Velocity​: A vector quantity that is a measure of the rate of change of

1.3 Mass and Weight

Balance​: ​A piece of apparatus that can compare different weights to demonstrate

Density​: ​The mass per unit volume of an object.

Displacement​: ​It is the object's overall change in position.​ ​Calculated by the

1.5.1 Effects of Forces

Air resistance:​ ​The resistance of an object’s motion through air. It is a form of

Extension–load graphs​: ​A graph that shows how the extension of an object

Hooke’s law ​: The extension of a spring is directly proportional to the force

Limit of proportionality​: The point beyond which the extension of an elastic

Spring constant:​ A measure of a spring’s stiffness. The higher the spring

1.5.2 Turning Effect

Principle of moments​:​ For an object in equilibrium, the sum of the clockwise

1.5.3 Conditions for Equilibrium

Turning effect​:​ It is also known as the moment of the force.

1.5.4 Centre of Mass

Plane lamina​:​ A body whose mass is concentrated in a single plane.

Stability​: ​A measure of the likelihood of an object toppling. An object is unstable if

Scalars​:​ ​Quantities that only have a magnitude, not a direction.

Conservation of momentum​:​ ​The total momentum of a system before an

Impulse​: The change of a system’s momentum as a result of a force acting

Momentum​: The product of an object’s mass and velocity.

1.7 Energy, Work and Power

Elastic potential (strain) energy:​ The store of energy that stretched or

Electrical current​: ​An electric current is a flow of electric charge in a circuit.

1.7.2 Energy Resources

Geothermal energy​: ​Renewable energy generated from the conversion of the

Hydroelectric power:​ Renewable energy generated by water stored at a height,

Manometer​: ​A U-shaped tube of liquid that allows the pressure on a column of

Mercury barometer​: ​A measuring device that measures changes in atmospheric

Pressure​: ​The force acting perpendicular to a surface, per unit area.

Topic 2: Thermal Physics

Definitions in ​bold ​are for extended students only

2.1 Simple Kinetic Molecular Model of Matter

2.1.1 States of Matter

2.1.2 Molecular Model

Gas temperature​: ​The temperature of a gas is directly proportional to the average

Kinetic molecular model of matter​: States that matter is made up of particles

Pressure of a gas​: ​The perpendicular force(rate of change of momentum) per

Suspension:​ ​A state in which particles are dispersed throughout a fluid.

Definitions in bold are for extended students only

Digital device: A measuring device that displays the measurement on a display,

Distance: A measure of how far an object moves. It doesn’t depend on direction

Micrometer screw gauge: A measuring implement used to accurately

Pendulum: A pendulum is a weight suspended from a pivot so that it can swing

Volume: The amount of space that a substance or object occupies.

Acceleration: The rate of change of velocity. It can be calculated from the

Air resistance: The resistance of an object’s motion through air. It is a form

Average speed: The average speed is calculated by dividing the distance

Deceleration: Negative acceleration.

Free fall: Motion under the force of gravity alone.

Speed: A scalar quantity that is a measure of the rate of change of distance.

Terminal velocity: Steady speed achieved by an object freely falling through

Gravitational field: A region where a mass will experience a non-contact

Velocity: A vector quantity that is a measure of the rate of change of

Balance: A piece of apparatus that can compare different weights to demonstrate

Density: The mass per unit volume of an object.

Displacement: It is the object's overall change in position. Calculated by the

Air resistance: The resistance of an object’s motion through air. It is a form of

Extension–load graphs: A graph that shows how the extension of an object

Hooke’s law : The extension of a spring is directly proportional to the force

Limit of proportionality: The point beyond which the extension of an elastic

Spring constant: A measure of a spring’s stiffness. The higher the spring

Principle of moments: For an object in equilibrium, the sum of the clockwise

Turning effect: It is also known as the moment of the force.

Plane lamina: A body whose mass is concentrated in a single plane.

Stability: A measure of the likelihood of an object toppling. An object is unstable if

Scalars: Quantities that only have a magnitude, not a direction.

Conservation of momentum: The total momentum of a system before an

Impulse: The change of a system’s momentum as a result of a force acting

Momentum: The product of an object’s mass and velocity.

Elastic potential (strain) energy: The store of energy that stretched or

Electrical current: An electric current is a flow of electric charge in a circuit.

Geothermal energy: Renewable energy generated from the conversion of the

Hydroelectric power: Renewable energy generated by water stored at a height,

Manometer: A U-shaped tube of liquid that allows the pressure on a column of

Mercury barometer: A measuring device that measures changes in atmospheric

Pressure: The force acting perpendicular to a surface, per unit area.

Definitions in bold are for extended students only

Gas temperature: The temperature of a gas is directly proportional to the average

Kinetic molecular model of matter: States that matter is made up of particles

Pressure of a gas: The perpendicular force(rate of change of momentum) per

Suspension: A state in which particles are dispersed throughout a fluid.

Evaporative cooling: It is cooling due to evaporation due to the escape of

Molecule: It is a particle made up of two or more atoms that are chemically

Temperature: A measure of the average kinetic energy of the particles in a

Volume of a gas: It is the quantity of three-dimensional space occupied by a gas.

Application: The action of putting something into operation.

Magnitude: A numerical quantity or value.

Thermal expansion: Thermal expansion is the increase, or decrease, of the size

Fixed points: A well-defined reproducible temperature which can be used as a

Liquid-in-glass thermometer: An instrument for measuring and indicating

Linearity of a thermometer: It is the property in a thermometer defined as the

Measurement: It is the process of associating numbers with physical quantities.

Range of a thermometer: It is the difference between the maximum and

Sensitivity of a thermometer: It is defined as the increase in the length of the

Specific heat capacity: The amount of energy needed to increase the

Thermal capacity: It is defined as the amount of heat to be supplied to a given

Condensation: The changing from vapour state to a liquid state, when a

Evaporation: Is the process by which an element or compound transitions

Latent heat: The energy required for a substance to change state.

Conduction: The transfer of heat energy through the vibrations of particles in a

Electron: A stable subatomic particle with a charge of negative electricity,

Thermal conductor: It is a material that allows energy in the form of heat, to be

Convection: The transfer of heat energy through convection currents in a fluid.

Electromagnetic spectrum: A group of transverse waves that cover a large

Conduction: The transfer of heat energy through the vibrations of particles in a

Convection: The transfer of heat energy through convection currents in a fluid.

Radiation: The emission of energy as electromagnetic waves or as moving

Definitions in bold are for extended students only

Amplitude: The maximum displacement of a wave from its undisturbed (equilibrium)

Reflection: The bouncing back of a wave at a boundary.

Vibration: Is a mechanical phenomenon whereby oscillations occur about an equilibrium

Water waves: They are waves propagating on the water surface.

Transparent: A material allowing light to pass through.

Diminished: Made smaller or less.

Enlarged: Having become or been made larger.

Single lens: A lens that consists of a single piece of transparent material.

Electromagnetic spectrum: A group of transverse waves that cover a large range of

Vacuum: Space in which there is no matter