Mini Physics
Part of Mini EducationSwitch subject
Search

All Definitions Needed For O Level

Key idea: Ace your O Level Physics exams with our free comprehensive definitions list. Ideal for O Level students.

  • SEC G3 Physics 2027
On this page

Learning objectives

  • Represent a physical quantity with a numerical magnitude and unit
  • Recall the six prescribed SI base quantities and their units
  • Use the prescribed SI prefixes from nano to tera
  • Compare orders of magnitude from a typical atom to the Earth
  • Select and justify measuring instruments by range and precision
  • Distinguish scalar and vector quantities and give examples
  • Add two vectors graphically to determine a resultant
  • State what speed means
  • State what velocity means, including its direction
  • Calculate average speed from total distance and total time
  • Calculate acceleration as change in velocity divided by time taken
  • State what uniform acceleration means
  • Interpret examples of non-uniform acceleration
  • Plot and interpret displacement–time and velocity–time graphs in one dimension
  • Deduce rest and uniform or non-uniform velocity from a displacement–time graph
  • Deduce rest, uniform velocity and uniform or non-uniform acceleration from a velocity–time graph
  • Use signed area under a velocity–time graph to determine displacement
  • Recall constant free-fall acceleration near Earth as approximately 10 m/s²
  • Distinguish contact forces from non-contact forces
  • State that mass measures the amount of matter in a body
  • Describe a gravitational field as a region where a mass experiences gravitational force
  • Define gravitational field strength as gravitational force per unit mass
  • Apply weight = mass × gravitational field strength
  • Distinguish mass from weight
  • Describe the effect of balanced and unbalanced forces on a body
  • Describe ways a force may change motion
  • Identify action–reaction pairs on interacting bodies
  • Draw free-body diagrams for force systems in at most two dimensions
  • Solve three-force static equilibrium graphically
  • Apply resultant force = mass × acceleration
  • Relate mass to resistance to change in motion
  • Explain the effects of friction on motion
  • Describe falling with and without air resistance, including terminal velocity
  • Describe a moment as a force's turning effect in everyday examples
  • Apply moment = force × perpendicular distance from the pivot
  • State the principle of moments for a body in equilibrium
  • apply the principle of moments to new situations or to solve related problems
  • show an understanding that the weight of a body may be taken as acting at a single point known as its centre of gravity
  • Explain qualitatively how centre-of-gravity position affects stability
  • Define pressure as force per unit area
  • Apply pressure = force ÷ area
  • Explain pressure transmission in a hydraulic press
  • Apply density = mass ÷ volume
  • Apply liquid-column pressure = height × density × gravitational field strength
  • Explain how liquid-column height measures atmospheric pressure
  • Explain how a manometer measures pressure difference
  • Recognise kinetic, potential, nuclear and internal energy stores
  • Describe mechanical energy transfer by a force acting over a distance
  • Describe electrical energy transfer by an electric current
  • Describe energy transfer by heating due to a temperature difference
  • Describe energy transfer by electromagnetic and mechanical waves
  • Recall and apply Ek = ½mv² in new situations
  • Recall and apply Ep = mgh near the Earth's surface in new situations
  • State and apply the principle of conservation of energy
  • Recall and apply work done = force × distance moved in the force direction
  • Recall and apply power = energy transfer / time taken
  • Calculate efficiency as useful energy output / total energy input
  • Evaluate prescribed electricity-generation resources by efficiency, cost, reliability and environmental impact
  • Compare physical properties of solids, liquids and gases
  • Explain state properties using particle arrangement, motion, forces and separation
  • Infer random molecular motion from a Brownian-motion experiment
  • Relate temperature rise to increased average kinetic energy of particles
  • Explain gas pressure using particle collisions with container walls
  • Explain heating from higher to lower temperature until thermal equilibrium
  • Describe conduction in solids through particle vibration and mobile electrons
  • Describe convection in fluids through density changes and bulk motion
  • Explain that energy transfer by electromagnetic radiation needs no material medium
  • Explain how surface colour, texture, temperature and area affect radiation transfer rate
  • Apply conduction, convection and radiation in everyday systems
  • describe internal energy as an energy store that is made up of the total kinetic energy associated with the random motion of the particles and the total potential energy between the particles in the system
  • Define heat capacity and specific heat capacity
  • Apply energy transferred = mass × specific heat capacity × temperature change
  • describe melting/solidification and boiling/condensation as processes of energy transfer without a change in temperature
  • Explain the difference between boiling and evaporation
  • Define latent heat and specific latent heat
  • Apply energy transferred for a change of state = mass × specific latent heat
  • Explain latent heat using particle behaviour
  • Sketch and interpret a cooling curve
  • Describe wave generation by vibrating sources, ropes and springs
  • Describe ripple-tank waves using wavefronts
  • Explain that waves transfer energy
  • Explain that wave energy transfer does not transfer matter
  • Use amplitude, frequency and wavelength to describe wave motion
  • Define and use wave speed and period and interpret wave graphs
  • Recall and apply wave speed = frequency × wavelength
  • Compare transverse and longitudinal waves and give examples
  • Explain sound production by vibration and the need for a medium
  • Describe sound using compressions and rarefactions
  • Relate sound loudness to amplitude and pitch to frequency
  • Explain reflected-sound echoes and use them to measure distance
  • Explain ultrasound use in sonar and soft-tissue scanning
  • State that all electromagnetic waves are transverse
  • State that all electromagnetic waves travel at the same speed in vacuum
  • Order the seven electromagnetic-spectrum regions
  • Relate spectrum order to wavelength and frequency
  • State typical uses of radio waves
  • State typical uses of microwaves
  • State typical uses of infrared
  • State typical uses of visible light
  • State typical uses of ultraviolet
  • State typical uses of X-rays
  • State typical uses of gamma rays
  • Describe hazardous heating effects of electromagnetic over-exposure
  • Describe hazardous ionising effects on living cells and tissue
  • Use the normal, angle of incidence and angle of reflection
  • Apply the law of reflection in constructions, measurements and calculations
  • Use the normal, angle of incidence and angle of refraction
  • Apply sin i divided by sin r as a constant for a fixed pair of media
  • Define refractive index as vacuum light speed divided by medium light speed
  • Explain the critical angle
  • Explain the conditions for total internal reflection
  • Apply total internal reflection to optical fibres and state advantages
  • Describe how a thin converging lens acts on a light beam
  • Define the focal length of a converging lens
  • Construct real and virtual image ray diagrams for a thin converging lens
  • Describe lens images as real or virtual, magnified or diminished, and upright or inverted
  • state that there are positive and negative charges and that charge is measured in coulombs
  • state that unlike charges attract and like charges repel
  • Describe an electric field as a region where charge experiences force
  • Recall that the field lines of an isolated point charge give the direction of the force on a positive test charge
  • Draw the directed electric field of an isolated point charge
  • Interpret the electric-field pattern between two isolated point charges
  • Draw the electric-field pattern between two isolated point charges
  • Explain charging by rubbing as electron transfer
  • Describe experiments that charge a conductor by induction
  • Describe potential electrostatic-charging hazards
  • Describe an electrostatic precipitator and transfer the principle
  • State current as rate of charge flow measured in amperes
  • Distinguish conventional current from electron flow
  • Apply charge equals current multiplied by time
  • Define source e.m.f. as work done per unit charge around a circuit
  • Calculate total e.m.f. for sources in series
  • Define component potential difference as work done per unit charge
  • State resistance as potential difference divided by current
  • Apply resistance equals potential difference divided by current
  • Apply wire-resistance proportionalities for length and cross-sectional area
  • Describe the effect of temperature on metallic resistance
  • Sketch and interpret required current–voltage characteristics
  • Recognise and interpret circuit symbols for cells, batteries, switches, lamps, LEDs, resistors, fuses, ammeters and voltmeters
  • Draw circuit diagrams with cells, batteries, switches, lamps, LEDs, fixed and variable resistors, fuses, ammeters and voltmeters
  • Recognise and interpret circuit symbols for d.c. and a.c. supplies, potentiometers, bells, light-dependent resistors and thermistors
  • Draw circuit diagrams with d.c. and a.c. supplies, potentiometers, bells, light-dependent resistors and thermistors
  • Apply the same-current rule in series circuits
  • Apply the potential-difference sum in series circuits
  • Apply current conservation at parallel junctions
  • Apply equal potential difference across parallel branches
  • Calculate effective resistance in series
  • Calculate effective resistance in parallel
  • Solve whole-circuit problems using consistent quantities
  • Describe variable-potential-divider action
  • Describe NTC thermistor action as an input transducer
  • Describe light-dependent resistor (LDR) action as an input transducer
  • Solve simple NTC and LDR potential-divider problems
  • Explain electrical heating in common appliances
  • Apply P = VI
  • Apply E = VIt
  • Calculate electrical energy and cost in kWh
  • Identify the hazard from damaged insulation
  • Identify the hazard from overheating cables
  • Identify the hazard from damp conditions
  • Explain how fuses and circuit breakers protect circuits
  • Choose and justify an appropriate fuse rating
  • Explain why metal casings are earthed
  • Explain why double-insulated appliances do not need an earth wire
  • State the meanings and roles of live, neutral and earth
  • Describe the wiring of a mains plug
  • Explain live-wire placement of switches, fuses and circuit breakers
  • State the properties of magnets
  • Describe induced magnetism
  • Distinguish temporary and permanent magnets
  • Determine magnetic-field direction with a compass or bar magnet
  • Interpret bar-magnet field patterns
  • Draw the magnetic field pattern around a bar magnet and between the poles of two bar magnets
  • Interpret the field pattern around a straight current-carrying wire
  • Draw the magnetic field pattern around a straight current-carrying wire
  • Interpret the field pattern around a current-carrying solenoid
  • Draw the magnetic field pattern around a current-carrying solenoid
  • Relate current magnitude and direction to magnetic field
  • Describe electromagnet applications
  • Describe experiments showing the force on a current-carrying conductor in a magnetic field
  • Describe magnetic force on a charged-particle beam
  • Predict force reversal when current or field reverses
  • Use Fleming’s left-hand rule
  • Explain the turning effect on a current-carrying coil
  • Explain how current and turns increase the turning effect
  • Describe split-ring commutator action
  • Describe the effect of winding a motor coil on a soft-iron cylinder
  • Deduce that a changing magnetic field can induce an e.m.f.
  • Deduce that induced e.m.f. opposes the change producing it
  • Deduce factors affecting induced e.m.f. magnitude
  • Describe a simple a.c. generator and slip rings
  • Sketch a simple a.c. generator voltage–time graph
  • Describe a simple iron-cored transformer
  • Apply ideal-transformer equations
  • Explain cable loss and high-voltage transmission
  • Describe atomic composition
  • Use proton number, nucleon number and isotope
  • Use and interpret nuclide notation
  • Explain random and spontaneous nuclear decay
  • Describe alpha, beta-minus and gamma radiation
  • Compare ionising effect and penetrating power
  • Use nuclide equations for radioactive decay
  • Explain background radiation
  • Use half-life in tables and decay curves
  • State radioactivity applications and hazards
  • Evaluate uses and hazards using half-life and radiation properties
  • Relate fission and fusion to nuclear-energy release
  • Measurements of length, mass, temperature, time interval, volume of liquids/solids and force (e.g. weight) using appropriate instruments
  • Determination of the density of a liquid, or of a regularly or irregularly shaped solid that sinks in water
  • Determination of the value of the acceleration of free fall
  • Investigation of the effects of balanced and unbalanced forces
  • The principle of moments
  • Determination of the position of the centre of gravity of a plane lamina
  • Investigation of the factors affecting transfer of energy by thermal processes
  • Determination of heat capacities of materials
  • Latent heat of substances
  • The law of reflection
  • Determination of the position and characteristics of an optical image formed by a plane mirror or a thin converging lens
  • The refraction of light through glass blocks
  • The principle of total internal reflection
  • The focal length of lenses
  • Determination of the speed, wavelength and frequency of waves
  • Determination of the resistance of a circuit component
  • Investigation of the magnetic effect of current in a conductor
  • Investigation of the effects of electromagnetic induction

This post contains the key definitions you need for GCE O Level Physics (6091).

Use it alongside:

Not required for 6091 (common extensions)

Some topics appear in other syllabuses or in enrichment pages but are not required for O Level Physics (6091). Examples:

  • Boyle’s law (gas law)
  • Upthrust (buoyancy) and Archimedes’ principle

1. Measurement & Mechanics

Measurement

  • A physical quantity is a measurable property that has a number and a unit.
  • A base quantity is chosen and defined independently (not derived from other quantities).
  • A derived quantity is defined from base quantities (e.g. by products/quotients/powers).
  • A scalar has magnitude only.
  • A vector has magnitude and direction.
  • Accuracy is how close a measurement is to the true value.
  • Precision is how close repeated measurements are to each other.
  • A random error causes scatter in readings (varies from reading to reading).
  • A systematic error shifts readings in one direction (consistent bias).
  • A zero error is a non-zero reading when the true value is zero (a type of systematic error).
  • Parallax error is a reading error caused by viewing a scale from the wrong angle.

Kinematics

  • Distance is the length of the path travelled.
  • Displacement is the straight-line change in position from start to finish (with direction).
  • Speed is distance travelled per unit time.
  • Velocity, v, is the rate of change of displacement with time.
  • Acceleration, a, is the rate of change of velocity with time.

Dynamics + Turning Effect

  • A force is a push or pull that can change motion or shape.
  • The resultant force is the single force that has the same effect as all the forces acting together.
  • Balanced forces give zero resultant force (no change in velocity).
  • Unbalanced forces give a non-zero resultant force (velocity changes).
  • Newton’s First Law: an object stays at rest or moves with constant velocity in a straight line unless a resultant force acts.
  • Newton’s Second Law: acceleration is proportional to resultant force and inversely proportional to mass; acceleration is in the direction of the resultant force.
  • Newton’s Third Law: if A exerts a force on B, B exerts an equal and opposite force on A (on a different body).
  • The moment of a force (torque) about a pivot is the product of the force and the perpendicular distance from the pivot to the line of action of the force.
  • The centre of mass is the point where the mass of a body may be considered to be concentrated.
  • The centre of gravity is the point where the weight of a body may be considered to act.

Mass, Weight & Gravity

  • Mass, m (kg), is the amount of matter in an object.
  • Weight, W (N), is the gravitational force on an object.
  • Inertia is the tendency of an object to resist a change in its motion (depends on mass).
  • A gravitational field is a region where a mass experiences a force due to gravity.
  • Gravitational field strength, g (N kg⁻¹), is gravitational force per unit mass.
  • Terminal velocity is the constant velocity reached when resistive force equals weight in free fall.

Pressure

  • Pressure, p (Pa), is the normal force per unit area: p = F/A.
  • Density, ρ (kg m⁻³), is mass per unit volume: ρ = m/V.
  • Hydrostatic pressure is the pressure in a liquid due to the weight of the liquid above a point (increases with depth).

Work, Energy & Power

  • Work done, W (J), is energy transferred when a force moves an object through a distance in the direction of the force.
  • The principle of conservation of energy: energy cannot be created or destroyed; it is converted from one form to another; the total energy of a closed system remains constant.
  • Kinetic energy, Eₖ (J), is energy due to motion.
  • Gravitational potential energy is energy due to height in a gravitational field.
  • Power, P (W), is the rate of energy transfer (or rate of doing work): P = E/t.
  • Efficiency is: (useful output)/(total input) × 100% (using either energy or power).

2. Thermal Physics & Waves

Thermal Physics

  • Temperature is a measure of the degree of hotness (linked to the average kinetic energy of particles).
  • Thermal equilibrium is when two objects in contact are at the same temperature, so there is no net energy transfer between them by heating.
  • Internal energy is the total kinetic and potential energy of particles in a substance.
  • Melting is the change of state from solid to liquid at constant temperature (melting point).
  • Freezing / solidification is the change of state from liquid to solid at constant temperature.
  • Boiling is the change of state from liquid to gas throughout the liquid at the boiling point.
  • Evaporation is the change of state from liquid to gas at the surface, below the boiling point.
  • Condensation is the change of state from gas to liquid.
  • Heat capacity, C (J °C⁻¹), is the energy required to raise the temperature of a body by 1°C.
  • Specific heat capacity, c (J kg⁻¹ °C⁻¹), is the energy required to raise the temperature of 1 kg of a substance by 1°C.
  • Specific latent heat of fusion, l_f (J kg⁻¹), is the energy required to change 1 kg from solid to liquid without changing its temperature.
  • Specific latent heat of vaporisation, lᵥ (J kg⁻¹), is the energy required to change 1 kg from liquid to gas without changing its temperature.
  • Conduction transfers energy through a substance without bulk motion of the substance.
  • Convection transfers energy through the bulk movement of a fluid caused by density differences.
  • Thermal radiation transfers energy by electromagnetic waves, mainly infrared, and does not need a material medium.

Waves Hub

  • A wave is a travelling disturbance that transfers energy without transferring matter overall.
  • A transverse wave has oscillations perpendicular to the direction of travel.
  • A longitudinal wave has oscillations parallel to the direction of travel (compressions and rarefactions).
  • Amplitude is the maximum displacement from the equilibrium position.
  • Wavelength, λ, is the distance between two points in phase (e.g. crest to crest).
  • Frequency, f (Hz), is the number of complete waves passing a point per second.
  • Period, T (s), is the time for one complete wave.
  • Wave speed, v, is distance travelled per unit time; for waves: v = fλ.
  • Reflection is when a wave bounces off a surface and stays in the same medium.
  • Refraction is the change in direction of a wave due to a change in speed when entering a different medium.
  • Refractive index, n, is n = (sin i)/(sin r) (for a given pair of media), where i is angle of incidence and r is angle of refraction.
  • Total internal reflection is complete reflection inside a denser medium when the angle of incidence is greater than the critical angle.

3. Electricity & Magnetism

Static Electricity

  • Electric charge, Q (C), is a property of matter that causes electric forces.
  • An electric field is a region where an electric charge experiences an electric force.
  • Electric field lines show the direction of force on a positive test charge.
  • Charging by friction transfers electrons between materials by rubbing.
  • Charging by induction charges an object without contact, using a nearby charged object and earthing.
  • Earthing is connecting an object to the Earth so charge can flow to/from the ground.

Current Electricity

  • Electric current, I (A), is the rate of flow of charge: I = Q/t.
  • Potential difference (p.d.), V (V), is energy transferred per unit charge: V = E/Q.
  • Electromotive force (e.m.f.), ε (V), is energy supplied by a source per unit charge.
  • Resistance, R (Ω), is a measure of how much a component opposes current: R = V/I.
  • Ohm’s law: for a conductor at constant temperature, current is directly proportional to potential difference.
  • Electrical power, P (W), is the rate of electrical energy transfer: P = VI.
  • Electrical energy, E (J), transferred is E = Pt.

D.C. Circuits

  • A series circuit has one path for current (current is the same through each component).
  • A parallel circuit has branches (p.d. is the same across each branch).
  • A potential divider uses resistors in series to provide a fraction of the supply p.d. at a point.
  • An LDR is a light-dependent resistor: resistance decreases when light intensity increases.
  • A thermistor is a temperature-dependent resistor (NTC: resistance decreases when temperature increases).

Practical Electricity

  • A fuse is a safety device that melts and breaks the circuit if current exceeds a safe value.
  • A circuit breaker is a safety device that switches off the circuit if current is too large.
  • The live wire carries the supply potential; the neutral wire is at (approximately) zero potential.
  • The earth wire provides a low-resistance path to ground to reduce electric shock risk.
  • Double insulation protects users without an earth wire by using two layers of insulating material.

Magnetism & Electromagnetism

  • Magnetic poles are north and south; like poles repel and unlike poles attract.
  • A magnetic field is a region where a magnet (or magnetic material) experiences a force.
  • Magnetic field lines show the direction of the force on a north pole placed in the field.
  • An electromagnet is a magnet made by passing current through a coil (often with an iron core).
  • Magnetic effect of current: a current produces a magnetic field around a conductor.

Electromagnetic Induction

  • Electromagnetic induction is producing an e.m.f. (and current in a closed circuit) by changing magnetic flux linkage.
  • Faraday’s law: the induced e.m.f. is proportional to the rate of change of magnetic flux linkage.
  • Lenz’s law: the induced e.m.f. (and induced current) is in a direction that opposes the change producing it.

4. Radioactivity

Radioactivity & the Nuclear Atom

  • An atom has a nucleus (protons + neutrons) with electrons around it.
  • A nuclide is an atom with a specific number of protons and neutrons in its nucleus.
  • Isotopes are atoms of the same element (same proton number) with different numbers of neutrons.
  • Radioactive decay is a spontaneous, random process where an unstable nucleus emits radiation.
  • Alpha (α) particles are helium nuclei (2 protons + 2 neutrons).
  • Beta (β) particles are fast electrons.
  • Gamma (γ) rays are high-energy electromagnetic waves.
  • Half-life is the time taken for half the unstable nuclei in a sample to decay.
  • Activity (Bq) is the number of decays per second.
  • Background radiation is the radiation that is always present in the environment.

5. Paper 3 (Practical) Definitions

Practical Skills Hub

  • Repeatable results are consistent when the same person uses the same method and equipment.
  • Reproducible results are consistent when different people/methods/equipment are used.
  • Reliability is about how consistent measurements are (low scatter).
  • A best-fit line is a line/curve drawn to represent the overall trend of data.
  • The gradient is the slope of a straight-line graph: gradient = Δ y/Δ x.
  • A data-logger records sensor readings automatically (useful for reducing reaction-time error and collecting more data).

Proceed To O Level Formula List

Continue with the next resource in this course.

Course and syllabus information
Course
SEC G3 Physics
Edition
SEC G3 Physics 2027