Comprehensive Physics Notes for Cambridge IGCSE 0625 (2026-2028)

1.2 Motion

Core
- Speed is defined as distance travelled per unit time.
- $v = \frac{s}{t}$ , where:
  - v = speed
  - s = distance travelled
  - t = time taken
- Velocity is speed in a given direction.
- Average speed = total distance travelled / total time taken.
- Distance-time graphs and speed-time graphs can be sketched, plotted, and interpreted.
- Qualitatively determine from graphs or data when an object is:
  - At rest
  - Moving with constant speed
  - Accelerating
  - Decelerating
- Speed is calculated from the gradient of a straight-line section of a distance-time graph.
- The area under a speed-time graph gives the distance travelled for motion with constant speed or constant acceleration.
- The acceleration of free fall $g$ near the Earth's surface is approximately constant and is approximately $9.8 m/s^2$ .
Supplement
- Acceleration is defined as the change in velocity per unit time.
- $a = \frac{\Delta v}{\Delta t}$ , where:
  - $a$ = acceleration
  - $\Delta v$ = change in velocity
  - $\Delta t$ = change in time
- Determine from data or speed-time graph shape when an object is moving with:
  - Constant acceleration
  - Changing acceleration
- Acceleration is calculated from the gradient of a speed-time graph.
- Deceleration is negative acceleration and used in calculations.
- Describe the motion of objects falling in a uniform gravitational field with and without air/liquid resistance, including reference to terminal velocity.

1.3 Mass and weight

Core
- Mass is the measure of the quantity of matter in an object at rest relative to the observer.
- Weight is a gravitational force on an object that has mass.
- Gravitational field strength is defined as force per unit mass.
- $g = \frac{W}{m}$ , where:
  - $g$ = gravitational field strength
  - $W$ = weight
  - $m$ = mass
- This is equivalent to the acceleration of free fall.
- Weights (and masses) may be compared using a balance.
Supplement
- Weight as the effect of a gravitational field on a mass.

1.4 Density

Core
- Density is defined as mass per unit volume.
- $\rho = \frac{m}{V}$ , where:
  - $\rho$ = density
  - $m$ = mass
  - $V$ = volume
- Describe how to determine the density of a liquid, a regularly shaped solid, and an irregularly shaped solid which sinks in a liquid (volume by displacement), including appropriate calculations.
- Determine whether an object floats based on density data.
Supplement
- Determine whether one liquid will float on another liquid based on density data given that the liquids do not mix.

1.5 Forces

1.5.1 Effects of forces

Core
- Forces may produce changes in the size and shape of an object.
- Load-extension graphs for an elastic solid are sketched, plotted, and interpreted; describe associated experimental procedures.
- The resultant of two or more forces acting along the same straight line is determined.
- An object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force.
- Resultant force may change the velocity of an object by changing its direction of motion or its speed.
Supplement
- Spring constant is defined as force per unit extension.
- $k = \frac{F}{x}$ , where:
  - $k$ = spring constant
  - $F$ = force
  - $x$ = extension
- Define and use the term 'limit of proportionality' for a load-extension graph and identify this point on the graph (an understanding of the elastic limit is not required).
- $F = ma$ , where:
  - $F$ = force
  - $m$ = mass
  - $a$ = acceleration
- Force and acceleration are in the same direction.
- Describe, qualitatively, motion in a circular path due to a force perpendicular to the motion as:
  - Speed increases if force increases, with mass and radius constant.
  - Radius decreases if force increases, with mass and speed constant.
  - Increased mass requires an increased force to keep speed and radius constant.
  - ( $F = \frac{mv^2}{r}$ is not required)
Core
- Solid friction is described as the force between two surfaces that may impede motion and produce heating.
- Friction (drag) acts on an object moving through a liquid
- Friction (drag) acts on an object moving through a gas (e.g. air resistance).

1.5.2 Turning effect of forces

Core
- The moment of a force is described as a measure of its turning effect and give everyday examples.
- Moment of a force = force × perpendicular distance from the pivot.
- Apply the principle of moments to situations with one force each side of the pivot, including balancing of a beam.
- When there is no resultant force and no resultant moment, an object is in equilibrium.
Supplement
- Apply the principle of moments to other situations, including those with more than one force each side of the pivot.
- Describe an experiment to demonstrate that there is no resultant moment on an object in equilibrium.

1.5.3 Centre of gravity

Core
- State what is meant by centre of gravity.
- Describe an experiment to determine the position of the centre of gravity of an irregularly shaped plane lamina.
- Describe, qualitatively, the effect of the position of the centre of gravity on the stability of simple objects.

1.6 Momentum

Supplement
- Momentum is defined as mass × velocity.
- $p = mv$ , where:
  - $p$ = momentum
  - $m$ = mass
  - $v$ = velocity
- Impulse is defined as force × time for which force acts.
- $impulse = F\Delta t = \Delta (mv)$
- Apply the principle of the conservation of momentum to solve simple problems in one dimension.
- Resultant force is defined as the change in momentum per unit time.
- $F = \frac{\Delta p}{\Delta t}$

1.7 Energy, work and power

1.7.1 Energy

Core
- Energy may be stored as kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal).
- Describe how energy is transferred between stores during events and processes, including examples of transfer by forces (mechanical work done), electrical currents (electrical work done), heating, and by electromagnetic, sound and other waves.
- Know the principle of the conservation of energy and apply this principle to simple examples including the interpretation of simple flow diagrams.
Supplement
- $E_k = \frac{1}{2}mv^2$
  - $E_k$ = kinetic energy
  - $m$ = mass
  - $v$ = velocity
- $\Delta E_p = mg\Delta h$
  - $\Delta E_p$ = change in gravitational potential energy
  - $m$ = mass
  - $g$ = gravitational field strength
  - $\Delta h$ = change in height
- Know the principle of the conservation of energy and apply this principle to complex examples involving multiple stages, including the interpretation of Sankey diagrams.

1.7.2 Work

Core
- Mechanical or electrical work done is equal to the energy transferred.
- $W = Fd = \Delta E$ , where:
  - $W$ = work done
  - $F$ = force
  - $d$ = distance
  - $\Delta E$ = change in energy

1.7.3 Energy resources

How useful energy may be obtained, or electrical power generated, from:
- Chemical energy stored in fossil fuels
- Chemical energy stored in biofuels
- Water, including the energy stored in waves, in tides and in water behind hydroelectric dams
- Geothermal resources
- Nuclear fuel
- Light from the Sun to generate electrical power (solar cells)
- Infrared and other electromagnetic waves from the Sun to heat water (solar panels) and be the source of wind energy including references to a boiler, turbine and generator where they are used.
- Describe advantages and disadvantages of each method in terms of renewability, availability, reliability, scale and environmental impact
Core
- Understand, qualitatively, the concept of efficiency of energy transfer.
Supplement
- Radiation from the Sun is the main source of energy for all our energy resources except geothermal, nuclear and tidal.
- Energy is released by nuclear fusion in the Sun.
- Research is being carried out to investigate how energy released by nuclear fusion can be used to produce electrical energy on a large scale.
- $(%) \text{ efficiency } = \frac{\text{useful energy output}}{\text{total energy input}} (\times 100%)$
- $(%) \text{ efficiency } = \frac{\text{useful power output}}{\text{total power input}} (\times 100%)$

1.7.4 Power

Core
- Power is defined as work done per unit time and also as energy transferred per unit time.
  - $P = \frac{W}{t}$
  - $P = \frac{\Delta E}{t}$
    - $P$ = power
    - $W$ = work done
    - $\Delta E$ = change in energy
    - $t$ = time

1.8 Pressure

Core
- Pressure is defined as force per unit area.
  - $p = \frac{F}{A}$
    - $p$ = pressure
    - $F$ = force
    - $A$ = area
- Describe how pressure varies with force and area in the context of everyday examples.
- Describe, qualitatively, how the pressure beneath the surface of a liquid changes with depth and density of the liquid.
Supplement
- $\Delta p = \rho g \Delta h$
  - $\Delta p$ = change in pressure
  - $\rho$ = density
  - $g$ = gravitational field strength
  - $\Delta h$ = change in depth

2 Thermal physics

2.1 Kinetic particle model of matter

2.1.1 States of matter

Core
- Know the distinguishing properties of solids, liquids and gases.
- Know the terms for the changes in state between solids, liquids and gases (gas to solid and solid to gas transfers are not required).

2.1.2 Particle model

Core
- Describe the particle structure of solids, liquids and gases in terms of the arrangement, separation and motion of the particles and represent these states using simple particle diagrams.
- Describe the relationship between the motion of particles and temperature, including the idea that there is a lowest possible temperature (-273°C), known as absolute zero, where the particles have least kinetic energy.
- Describe the pressure and the changes in pressure of a gas in terms of the motion of its particles and their collisions with a surface.
- Know that the random motion of microscopic particles in a suspension is evidence for the kinetic particle model of matter.
- Describe and explain this motion (sometimes known as Brownian motion) in terms of random collisions between the microscopic particles in a suspension and the particles of the gas or liquid.
Supplement
- Know that the forces and distances between particles (atoms, molecules, ions and electrons) and the motion of the particles affects the properties of solids, liquids and gases.
- Describe the pressure and the changes in pressure of a gas in terms of the forces exerted by particles colliding with surfaces, creating a force per unit area.
- Know that microscopic particles may be moved by collisions with light fast-moving molecules and correctly use the terms atoms or molecules as distinct from microscopic particles.

2.1.3 Gases and the absolute scale of temperature

Core
- Describe qualitatively, in terms of particles, the effect on the pressure of a fixed mass of gas of:
  - a change of temperature at constant volume
  - a change of volume at constant temperature
- Convert temperature between kelvin and degrees Celsius.
  - $T (in K) = \theta (in \degree C) + 273$
Supplement
- $pV = constant$

2.2 Thermal properties and temperature

2.2.1 Thermal expansion of solids, liquids and gases

Core
- Describe, qualitatively, the thermal expansion of solids, liquids and gases at constant pressure.
- Describe some of the everyday applications and consequences of thermal expansion.
Supplement
- Explain, in terms of the motion and arrangement of particles, the relative order of magnitudes of the expansion of solids, liquids and gases as their temperatures rise.

2.2.2 Specific heat capacity

Core
- Know that a rise in the temperature of an object increases its internal energy
Supplement
- Describe an increase in temperature of an object in terms of an increase in the average kinetic energies of all of the particles in the object.
- Define specific heat capacity as the energy required per unit mass per unit temperature increase.
- $c = \frac{\Delta E}{m \Delta \theta}$
  - c = specific heat capacity
  - $\Delta E$ = change in energy
  - m = mass
  - $\Delta \theta$ = change in temperature
- Describe experiments to measure the specific heat capacity of a solid and a liquid.

2.2.3 Melting, boiling and evaporation

Core
- Describe melting and boiling in terms of energy input without a change in temperature.
- Know the melting and boiling temperatures for water at standard atmospheric pressure.
- Describe condensation and solidification in terms of particles.
- Describe evaporation in terms of the escape of more-energetic particles from the surface of a liquid.
- Know that evaporation causes cooling of a liquid.
Supplement
- Describe the differences between boiling and evaporation.
- Describe how temperature, surface area and air movement over a surface affect evaporation.
- Explain the cooling of an object in contact with an evaporating liquid.

2.3 Transfer of thermal energy

2.3.1 Conduction

Core
- Describe experiments to demonstrate the properties of good thermal conductors and bad thermal conductors (thermal insulators).
Supplement
- Describe thermal conduction in all solids in terms of atomic or molecular lattice vibrations and also in terms of the movement of free (delocalised) electrons in metallic conductors.
- Describe, in terms of particles, why thermal conduction is bad in gases and most liquids.
- Know that there are many solids that conduct thermal energy better than thermal insulators but do so less well than good thermal conductors.

2.3.2 Convection

Core
- Know that convection is an important method of thermal energy transfer in liquids and gases.
- Explain convection in liquids and gases in terms of density changes and describe experiments to illustrate convection.

2.3.3 Radiation

Core
- Know that thermal radiation is infrared radiation and that all objects emit this radiation.
- Know that thermal energy transfer by thermal radiation does not require a medium.
- Describe the effect of surface colour (black or white) and texture (dull or shiny) on the emission, absorption and reflection of infrared radiation.
Supplement
- Know that for an object to be at a constant temperature it needs to transfer energy away from the object at the same rate that it receives energy.
- Know what happens to an object if the rate at which it receives energy is less or more than the rate at which it transfers energy away from the object.
- Know how the temperature of the Earth is affected by factors controlling the balance between incoming radiation and radiation emitted from the Earth’s surface.
Supplement
- Describe experiments to distinguish between good and bad emitters of infrared radiation.
- Describe experiments to distinguish between good and bad absorbers of infrared radiation.
- Describe how the rate of emission of radiation depends on the surface temperature and surface area of an object.

2.3.4 Consequences of thermal energy transfer

Core
- Explain some of the basic everyday applications and consequences of conduction, convection and radiation, including:
  - heating objects such as kitchen pans
  - heating a room by convection
Supplement
- Explain some of the complex applications and consequences of conduction, convection and radiation where more than one type of thermal energy transfer is significant, including:
  - a fire burning wood or coal
  - a radiator in a car

3 Waves

3.1 General properties of waves

Core
- Know that waves transfer energy without transferring matter.
- Describe what is meant by wave motion as illustrated by vibrations in ropes and springs, and by experiments using water waves.
- Describe the features of a wave in terms of wavefront, wavelength, frequency, crest (peak), trough, amplitude and wave speed.
- $v = f \lambda$
  - v = wave speed
  - f = frequency
  - $\lambda$ = wavelength
- Know that for a transverse wave, the direction of vibration is at right angles to the direction of propagation and understand that electromagnetic radiation, water waves and seismic S-waves (secondary) can be modelled as transverse

4.2 Electrical quantities

4.2.1 Electric charge

Core
- State that there are positive and negative charges
- State that positive charges repel other positive charges, negative charges repel other negative charges, but positive charges attract negative charges
- Describe simple experiments to show the production of electrostatic charges by friction and to show the detection of electrostatic charges
- Explain that charging of solids by friction involves only a transfer of negative charge (electrons)
- Describe an experiment to distinguish between electrical conductors and insulators
- Recall and use a simple electron model to explain the difference between electrical conductors and insulators and give typical examples
Supplement
- State that charge is measured in coulombs
- Describe an electric field as a region in which an electric charge experiences a force
- State that the direction of an electric field at a point is the direction of the force on a positive charge at that point
- Describe simple electric field patterns, including the direction of the field:
  - around a point charge
  - around a charged conducting sphere
  - between two oppositely charged parallel conducting plates (end effects will not be examined)

4.2.2 Electric current

Core
- Know that electric current is related to the flow of charge
- Describe the use of ammeters (analogue and digital) with different ranges
- Describe electrical conduction in metals in terms of the movement of free electrons
- Know the difference between direct current (d.c.) and alternating current (a.c.)
Supplement
- Define electric current as the charge passing a point per unit time
  - $I = \frac{Q}{t}$
    - I = electric current
    - Q = charge
    - t = time
- State that conventional current is from positive to negative and that the flow of free electrons is from negative to positive

4.2.3 Electromotive force and potential difference

Core
- Define electromotive force (e.m.f.) as the electrical work done by a source in moving a unit charge around a complete circuit
- Know that e.m.f. is measured in volts (V)
- Define potential difference (p.d.) as the work done by a unit charge passing through a component
- Know that the p.d. between two points is measured in volts (V)
- Describe the use of voltmeters (analogue and digital) with different ranges
Supplement
- $E = \frac{W}{Q}$
  - E = electromotive force (e.m.f.)
  - W = work done
  - Q = charge
- $V = \frac{W}{Q}$
  - V = potential difference (p.d.)
  - W = work done
  - Q = charge

4.2.4 Resistance

Core
- $R = \frac{V}{I}$
  - R = resistance
  - V = potential difference (p.d.)
  - I = electric current
- Describe an experiment to determine resistance using a voltmeter and an ammeter and do the appropriate calculations
- State, qualitatively, the relationship of the resistance of a metallic wire to its length and to its cross-sectional area
Supplement
- Sketch and explain the current–voltage graphs for a resistor of constant resistance, a filament lamp and a diode
- Recall and use the following relationship for a metallic electrical conductor:
  - resistance is directly proportional to length
  - resistance is inversely proportional to cross-sectional area

4.2.5 Electrical energy and electrical power

Core
- Understand that electric circuits transfer energy from a source of electrical energy, such as an electrical cell or mains supply, to the circuit components and then into the surroundings
- $P = IV$
- $E = IVt$
  - P = electrical power
  - I = electric current
  - V = potential difference (p.d.)
  - E = electrical energy
  - t = time
- Define the kilowatt-hour (kWh) and calculate the cost of using electrical appliances where the energy unit is the kWh

4.3 Electric circuits

4.3.1 Circuit diagrams and circuit components

Core
- Draw and interpret circuit diagrams containing cells, batteries, power supplies, generators, potential dividers, switches, resistors (fixed and variable), heaters, thermistors (NTC only), light- dependent resistors (LDRs), lamps, motors, bells, ammeters, voltmeters, magnetising coils, transformers, fuses and relays and know how these components behave in the circuit
Supplement
- Draw and interpret circuit diagrams containing diodes and light-emitting diodes (LEDs) and know how these components behave in the circuit

4.3.2 Series and parallel circuits

Core
- Know that the current at every point in a series circuit is the same
- Know how to construct and use series and parallel circuits
- Calculate the combined e.m.f. of several sources in series
- Calculate the combined resistance of two or more resistors in series
- State that, for a parallel circuit, the current from the source is larger than the current in each branch
- State that the combined resistance of two resistors in parallel is less than that of either resistor by itself
- State the advantages of connecting lamps in parallel in a lighting circuit
Supplement
- Recall and use in calculations, the fact that:
  - the sum of the currents entering a junction in a parallel circuit is equal to the sum of the currents that leave the junction
  - the total p.d. across the components in a series circuit is equal to the sum of the individual p.d.s across each component
  - the p.d. across an arrangement of parallel resistances is the same as the p.d. across one branch in the arrangement of the parallel resistances
Explain that the sum of the currents into a junction is the same as the sum of the currents out of the junction
Calculate the combined resistance of two resistors in parallel

4.3.3 Action and use of circuit components

Core
- Know that the p.d. across an electrical conductor increases as its resistance increases for a constant current
Supplement
- Describe the action of a variable potential divider
 - $\frac{R1}{R2} = \frac{V1}{V2}$
 - $R1, R2$ = resistors
 - $V1, V2$ = Potential divider

4.4 Electrical safety

Core
- State the hazards of:
  - damaged insulation
  - overheating cables
  - damp conditions
  - excess current from overloading of plugs, extension leads, single and multiple sockets when using a mains supply
- Know that a mains circuit consists of a live wire (line wire), a neutral wire and an earth wire and explain why a switch must be connected to the live wire for the circuit to be switched off safely
- Explain the use and operation of trip switches and fuses and choose appropriate fuse ratings and trip switch settings
- Explain why the outer casing of an electrical appliance must be either non-conducting (double-insulated) or earthed
- State that a fuse without an earth wire protects the circuit and the cabling for a double- insulated appliance