IGCSE Physics (0625)
Syllabus Notes (2026-2028)

Syllabus Alignment Notice: These notes strictly follow the Cambridge Assessment International Education (CAIE) syllabus for 2026, 2027, and 2028. Absolute Zero is evaluated at \(-273^\circ\text{C}\), the acceleration of free fall \(g\) is defined as \(9.8 \, \text{m/s}^2\), and the newly structurally detailed Unit 6 (Space Physics) is comprehensively included.

1. Motion, Forces and Energy

Mechanics describes the relationship between mass, velocity, acceleration, and forces within an structural framework.

1.1 Physical Quantities: Vectors and Scalars

  • Scalar Quantities: Have magnitude only. Examples: Distance, speed, time, mass, energy, temperature.
  • Vector Quantities: Have magnitude and direction. Examples: Displacement, velocity, acceleration, force, weight, momentum.

To determine a resultant force graphically or algebraically at right angles, apply the Pythagorean theorem and trigonometric tracking equations.

1.2 Motion (Kinematics)

Graph Type Gradient Represents Area Under Curve Represents
Distance-Time Graph Speed (\(v\)) N/A
Speed-Time Graph Acceleration (\(a\)) Distance Travelled (\(s\))
Average Speed: \(v = \frac{s}{t}\)
Acceleration: \(a = \frac{\Delta v}{t} = \frac{v - u}{t}\)
Acceleration of Free Fall: \(g = 9.8 \, \text{m/s}^2\)

1.3 Mass, Weight, and Density

  • Mass: A measure of the quantity of matter in an object; it remains constant everywhere and resists change in motion (inertia).
  • Weight: The gravitational force acting on an object variant by gravitational strength position.
Weight: \(W = mg\)
Density: \(\rho = \frac{m}{V}\)

1.4 Hooke's Law and Resultant Forces

Forces change the size, shape, or structural velocity profile of bodies. Hooke's Law states that extension is directly proportional to the applied load up to the limit of proportionality.

Hooke's Law: \(F = kx\)
Newton's Second Law: \(F = ma\)

1.5 Turning Effects and Momentum

The moment of a force is its turning effect about a fixed pivot point.

Moment: \(\text{Moment} = F \times d\) (where \(d\) is the perpendicular distance to the pivot)
Momentum: \(p = mv\)
Impulse / Change in Momentum: \(\text{Impulse} = \Delta p = F\Delta t = mv - mu\)
Principle of Moments: For a system in equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments. The system must also have zero net resultant force.

1.6 Work, Energy, Power, and Pressure

Energy cannot be created or destroyed, only transferred between storage states.

Kinetic Energy: \(E_k = \frac{1}{2}mv^2\)
Gravitational Potential Energy: \(\Delta E_p = mgh\)
Work Done: \(W = Fd = \Delta E\)
Power: \(P = \frac{W}{t} = \frac{\Delta E}{t}\)
Efficiency: \(\text{Efficiency} = \frac{\text{Useful Energy Output}}{\text{Total Energy Input}} \times 100\%\)
Solid Pressure: \(p = \frac{F}{A}\)
Liquid Hydrostatic Pressure: \(p = \rho gh\)

2. Thermal Physics

Deals with heat capacities, macroscopic expansion parameters, and kinetic particle configurations.

2.1 Kinetic Particle Model of Matter

  • Solids: High density, fixed volume and shape. Strong intermolecular bonds; particles vibrate about fixed positions.
  • Liquids: High density, fixed volume, variable shape. Weaker bonds; particles slide past one another.
  • Gases: Low density, variable shape and volume. Negligible intermolecular interactions; rapid, random straight-line motion.

2.2 Temperature and Thermal Expansion

As thermal kinetic profiles rise, average molecular spacing increases, producing structural volumetric expansions.

Kelvin Scale Conversion: \(T \text{ (in K)} = \theta \text{ (in }^\circ\text{C)} + 273\)
Boyle's Law for Ideal Gases: \(p_1V_1 = p_2V_2\) (at constant temperature)

2.3 Thermal Properties and Specific Heat Capacity

Specific Heat Capacity (\(c\)): The thermal energy required per unit mass to increase the temperature of a material by \(1^\circ\text{C}\).
Thermal Energy Equation: \(\Delta E = mc\Delta\theta\)

During a state change (melting or boiling), temperature remains completely constant as thermal energy works exclusively to break intermolecular bonds (latent heat processing).

2.4 Thermal Energy Transfers

  • Conduction: Thermal energy transfer through atomic lattice vibrations and free electron diffusion in metals.
  • Convection: Transfer in fluids via density fluctuations (heated fluid expands, becomes less dense, and rises, creating a convection current).
  • Radiation: Energy transfer via infrared electromagnetic radiation without requiring a physical medium. Dull, matte black surfaces are the best absorbers and emitters; shiny, silver surfaces are the best reflectors.

3. Properties of Waves

Waves transfer energy through space and materials without transferring matter particles.

3.1 Wave Characteristics

  • Transverse Waves: Vibration is perpendicular to the direction of energy travel. Examples: Light, EM waves, seismic S-waves.
  • Longitudinal Waves: Vibration is parallel to the direction of energy travel. Examples: Sound waves, seismic P-waves. Composed of compressions (high pressure) and rarefactions (low pressure).
The Wave Equation: \(v = f\lambda\)
Frequency / Period Relation: \(f = \frac{1}{T}\)

3.2 Reflection, Refraction, and Light Optics

When light crosses an optical boundary, its speed and wavelength shift, while its frequency remains constant.

Law of Reflection: \(\text{Angle of Incidence } (i) = \text{Angle of Reflection } (r)\)
Refractive Index: \(n = \frac{\sin i}{\sin r} = \frac{c}{v}\)
Critical Angle Equation: \(\sin c = \frac{1}{n}\)

Total Internal Reflection (TIR): Occurs exclusively when light travels from an optically denser medium to a less dense medium, and the angle of incidence exceeds the critical angle \(c\).

3.3 The Electromagnetic Spectrum

All EM waves are transverse and travel at the speed of light (\(c = 3.0 \times 10^8 \, \text{m/s}\)) in a vacuum.

Wave Type Main Practical Application Associated Danger
Radio Waves Radio/TV Communications None (Low energy)
Microwaves Satellite TV, Cooking Internal heating of body tissue
Infrared Remote controls, Thermal imaging Skin burns
Visible Light Vision, Fiber optics Eye damage from intense sources
Ultraviolet Sunbeds, Sterilization Skin cancer, Cataracts
X-Rays Medical imaging, Security check Cell mutation, Cancer induction
Gamma Rays Cancer radiotherapy, Sterilization Severe cellular damage, Mutation

3.4 Sound Waves

Sound waves are longitudinal mechanical waves that require a physical medium to travel through (\(v_{\text{solids}} > v_{\text{liquids}} > v_{\text{gases}}\)). The human hearing range is **20 Hz to 20,000 Hz (20 kHz)**; waves above 20 kHz are classified as ultrasound.

4. Electricity and Magnetism

Addresses electrical circuits, static phenomena, and electrodynamic induction laws.

4.1 Electrostatics and Circuits

Electric current represents the uniform rate of flow of electric charge.

Current: \(I = \frac{Q}{t}\)
Potential Difference / e.m.f.: \(V = \frac{W}{Q}\)
Ohm's Law (Resistance): \(R = \frac{V}{I}\)
Electrical Power: \(P = IV = I^2R = \frac{V^2}{R}\)
Electrical Energy: \(E = P \times t = IVt\)

4.2 Combined Resistance Rules

  • Series Circuits: Current is identical at all points. Total voltage is shared between components. Total resistance accumulates: \[ R_{\text{total}} = R_1 + R_2 + \dots \]
  • Parallel Circuits: Potential difference is identical across all branches. Total supply current splits across paths. Total resistance decreases: \[ \frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \dots \]

4.3 Electromagnetic Induction and Transformers

An electrical voltage induces across a conductor whenever it cuts across magnetic flux lines. Lenz's Law states that the direction of an induced current always opposes the change that caused it.

Transformer Voltage Ratio: \(\frac{V_p}{V_s} = \frac{N_p}{N_s}\)
100% Efficient Transformer Power Rule: \(I_p V_p = I_s V_s\)

5. Nuclear Physics

Atomic architecture, radioactive breakdown series, and isotopic stabilization trends.

5.1 The Nuclear Atom

Atoms are defined cleanly by matching numeric indicators: \({}_{Z}^{A}X\), where \(A\) is the Nucleon (Mass) Number, and \(Z\) is the Proton (Atomic) Number.

Isotopes: Atoms of the same element containing identical proton counts but variant nucleon (neutron) quantities.

5.2 Characteristics of Radioactive Decay Emissions

Radiation Type Structure Identity Ionizing Power Penetration Range
Alpha (\(\alpha\)) Helium nucleus (\({}_{2}^{4}\text{He}\)) Very High Low (Stopped by paper)
Beta (\(\beta\)) Fast electron (\({}_{-1}^{0}e\)) Medium Medium (Stopped by aluminum sheet)
Gamma (\(\gamma\)) High frequency EM wave Low Extremely High (Reduced by thick lead)
Alpha Decay Equation: \({}_{Z}^{A}X \longrightarrow {}_{Z-2}^{A-4}Y + {}_{2}^{4}\alpha\)
Beta Decay Equation: \({}_{Z}^{A}X \longrightarrow {}_{Z+1}^{A}Y + {}_{-1}^{0}\beta\)

Half-Life: The time required for half the active radioactive nuclei within a sample to decay to a more stable state.

6. Space Physics

Addresses orbital mechanics, planetary configurations, stellar lifetimes, and cosmological models.

6.1 Earth and the Solar System

The orbital speed of a astronomical body depends on its path radius and orbital period.

Orbital Velocity Formula: \(v = \frac{2\pi r}{T}\)

The Sun generates its vast energy through the **nuclear fusion** of hydrogen nuclei into helium inside its high-pressure core.

6.2 Stars and the Universe

Stars progress through predictable lifecycles dictated entirely by their starting birth mass:

  • Low-Mass Stars: Nebula \(\rightarrow\) Protostar \(\rightarrow\) Main Sequence \(\rightarrow\) Red Giant \(\rightarrow\) Planetary Nebula \(\rightarrow\) White Dwarf.
  • High-Mass Stars: Nebula \(\rightarrow\) Protostar \(\rightarrow\) Main Sequence \(\rightarrow\) Red Supergiant \(\rightarrow\) Supernova \(\rightarrow\) Neutron Star or Black Hole.

6.3 Light Redshift and the Expanding Universe

Light observed from distant galaxies shows an operational shift toward lower frequencies (longer wavelengths), known as redshift. This serves as key evidence that the universe is actively expanding outward from a single point of origin (The Big Bang Theory).

Hubble's Law: \(v = H_0 d\)
Current Syllabus Value for Hubble Constant: \(H_0 \approx 2.2 \times 10^{-18} \, \text{s}^{-1}\)