Cambridge IGCSE Physics (0625) – Core Syllabus Notes
Assessment Objectives (AOs)
- AO‑1: Knowledge and understanding of factual information, definitions and basic concepts.
- AO‑2: Application of knowledge – translate between words, symbols and diagrams; solve routine problems.
- AO‑3: Experimental skills – plan, carry out, analyse and evaluate investigations.
1. Motion, Forces & Energy (Unit 1)
1.1 Scalars & Vectors
- Scalar quantities have magnitude only (e.g. distance, speed, mass).
- Vector quantities have magnitude and direction (e.g. displacement, velocity, force).
- Resultant vector: use the tip‑to‑tail method or components.
1.2 Kinematics
| Quantity | Symbol | Unit | Formula (uniform motion) |
|---|
| Distance | s | m | – |
| Displacement | Δs | m | – |
| Speed | v | m s⁻¹ | v = s / t |
| Velocity | u | m s⁻¹ | u = Δs / t |
| Acceleration | a | m s⁻² | a = Δu / t |
Distance‑time and speed‑time graphs
- Slope of a distance‑time graph = speed (horizontal) or velocity (inclined).
- Area under a speed‑time graph = distance travelled.
- Gradient of a speed‑time graph = acceleration.
1.3 Forces & Newton’s Laws
- Resultant force, F = mass × acceleration (F = ma).
- Weight, W = mg (g = 9.8 m s⁻²).
- Frictional force, F_f = μ R (μ = coefficient of friction, R = normal reaction).
1.4 Momentum & Impulse
Momentum,
= mv. Impulse, J = FΔt = change in momentum.
1.5 Work, Energy & Power
- Work, W = F s cos θ (Joules).
- Kinetic energy, E_k = ½ mv².
- Gravitational potential energy, E_p = mgh.
- Power, P = W / t = F v (W = J s⁻¹).
1.6 Pressure
Pressure, p = F / A (Pa). In fluids, p = ρ g h where ρ = density, g = 9.8 m s⁻², h = depth.
2. Thermal Physics (Unit 2)
2.1 Kinetic Particle Model (AO‑1)
- All matter consists of tiny particles (atoms, molecules, ions) in constant motion.
- State‑dependent motion:
- Solids: particles vibrate about fixed positions in a regular lattice.
- Liquids: particles are close together, slide past one another.
- Gases: particles are far apart, move freely in all directions, colliding with each other and the container walls.
- Temperature measures the average kinetic energy of the particles.
- Absolute zero (0 K, –273 °C) is the theoretical point where particle motion ceases.
2.2 Brownian Motion – Direct Visual Evidence
When a dilute suspension of microscopic solid particles (e.g., pollen, chalk, milk fat) is placed in a liquid or gas, the particles jiggle erratically under a microscope. This is Brownian motion.
Why it supports the kinetic model
- The suspended particles are too large to be moved by any visible currents.
- Invisible molecules of the surrounding fluid, which are in constant random motion, collide with the suspended particles.
- Each collision transfers a tiny amount of momentum, causing a random change in direction.
- The cumulative effect of countless collisions produces the observed jittery path.
2.3 Quantitative Description (AO‑2)
- Mean‑square displacement: ⟨x²⟩ = 2 D t
- Diffusion coefficient: D = k_B T ⁄ (6π η r)
- k_B = 1.38 × 10⁻²³ J K⁻¹ (Boltzmann constant)
- T = absolute temperature (K)
- η = viscosity of the fluid (Pa s)
- r = radius of the suspended particle (m)
2.4 Heat Transfer & Specific Heat Capacity
| Concept | Formula | Units |
|---|
| Specific heat capacity | Q = mcΔθ | J kg⁻¹ K⁻¹ |
| Latent heat (fusion/evaporation) | Q = mL | J kg⁻¹ |
| Thermal expansion (linear) | ΔL = α L₀ Δθ | m |
| Thermal expansion (area) | ΔA = 2α A₀ Δθ | m² |
| Thermal expansion (volume) | ΔV = 3α V₀ Δθ | m³ |
2.5 Ideal‑Gas Relationships
- pV = nRT (combined gas law for a fixed amount of gas).
- At constant temperature, pV = constant (Boyle’s law).
- At constant pressure, V / T = constant (Charles’s law).
- At constant volume, p / T = constant (Gay‑Lussac’s law).
2.6 Temperature Conversions (AO‑2)
T(K) = θ(°C) + 273 θ(°C) = T(K) – 273
2.7 Practical Investigation – Brownian Motion (AO‑3)
Aim
To observe Brownian motion and investigate how temperature and viscosity affect its intensity, thereby providing experimental evidence for the kinetic particle model.
Materials
- Low‑power microscope (40×–100×)
- Glass slides & cover slips
- Suspension: fine chalk powder or milk in water (≈0.1 % w/v)
- Thermostated water bath (10 °C–60 °C)
- Viscous liquids for comparison (e.g., glycerol, syrup)
- Thermometer, stopwatch, reticle/grid
Method (summary)
- Prepare a thin film of the suspension on a slide and cover with a cover slip.
- Focus on a single particle; record its (x, y) coordinates every 2 s for 30 s.
- Repeat at three temperatures (e.g., 15 °C, 30 °C, 45 °C).
- Repeat the whole set using a more viscous fluid (e.g., glycerol) at a fixed temperature.
- Calculate successive displacements, plot displacement versus time, and determine the mean‑square displacement.
Variables
- Controlled: particle size, observation interval, magnification.
- Independent: temperature, fluid viscosity.
- Dependent: average displacement (or ⟨x²⟩) of the particle.
Safety
- Handle hot water baths with gloves.
- Never look directly at the microscope light source.
- Dispose of liquids according to school safety rules.
Sample Data Table
| Trial | Fluid | Temperature (°C) | Time (s) | Coordinates (x, y) mm | Δs (mm) |
|---|
Error‑analysis checklist
- Microscope resolution – can the particle’s centre be located accurately?
- Slide or stage drift during observation.
- Temperature stability of the bath.
- Variation in particle size within the suspension.
- Human reaction time when noting the time‑stamp.
3. Waves (Unit 3)
3.1 Wave Basics
- Wave speed: v = f λ (v = speed, f = frequency, λ = wavelength).
- Transverse waves – particle motion ⟂ to direction of travel (e.g., water surface waves, light).
- Longitudinal waves – particle motion ‖ direction of travel (e.g., sound).
3.2 Reflection & Refraction
- Law of reflection: angle of incidence = angle of reflection.
- Refraction: sin i / sin r = v₁ / v₂ = n₂ / n₁ (Snell’s law). n = refractive index.
3.3 Diffraction & Superposition
- Diffraction occurs when a wave passes an obstacle comparable to its wavelength – observed as spreading.
- Superposition: when two waves occupy the same region, resultant displacement = algebraic sum of individual displacements.
3.4 Sound
| Property | Typical value |
|---|
| Speed in air (20 °C) | ≈ 340 m s⁻¹ |
| Frequency range (human hearing) | 20 Hz – 20 kHz |
- Pitch ∝ frequency; loudness ∝ amplitude.
- Echoes occur when the reflecting surface is > 17 m away (time ≈ 0.1 s).
3.5 Electromagnetic (EM) Spectrum (brief)
Radio → Microwave → Infra‑red → Visible → Ultra‑violet → X‑ray → Gamma‑ray. All travel at c = 3 × 10⁸ m s⁻¹ in vacuum.
4. Electricity & Magnetism (Unit 4)
4.1 Electric Charge & Current
- Charge, q measured in coulombs (C). 1 C = 6.25 × 10¹⁸ electrons.
- Current, I = Δq ⁄ Δt (A = C s⁻¹).
4.2 Potential Difference & Resistance
- Potential difference (voltage), V = W ⁄ q (V = J C⁻¹).
- Resistance, R = V ⁄ I (Ω = V A⁻¹).
- Ohm’s law: V = IR (valid for ohmic conductors).
4.3 Power & Energy in Circuits
- P = VI = I²R = V² ⁄ R (W = J s⁻¹).
- Energy used, E = Pt (kWh = 3.6 MJ).
4.4 Series & Parallel Circuits
| Circuit type | Current | Voltage | Resistance |
|---|
| Series | Same through each component | Divides | R_total = ΣR |
| Parallel | Divides | Same across each branch | 1/R_total = Σ(1/R) |
4.5 Magnetic Fields
- Field lines emerge from north pole, enter south pole.
- Force on a current‑carrying conductor: F = B I L sin θ (B = magnetic flux density, T).
- Right‑hand rule for direction of B and force.
4.6 Electromagnetism
- Moving charge creates a magnetic field (Oersted’s experiment).
- Changing magnetic flux induces an emf (Faraday’s law): ε = – ΔΦ ⁄ Δt.
- Applications: electric motors (convert electrical energy → mechanical), generators (reverse), transformers (step‑up/step‑down voltage).
4.7 Safety & Practical Tips (AO‑3)
- Never touch live wires; use insulated tools.
- Fuse rating must be ≥ expected current.
- When measuring current, insert the ammeter in series; for voltage, connect voltmeter in parallel.
5. Nuclear Physics (Unit 5)
5.1 Atomic Structure & Radioactivity
- Atom = nucleus (protons + neutrons) + electrons.
- Isotopes: same Z (protons), different A (mass number).
- Radioactive decay types:
- α‑decay: emission of ⁴He nucleus (2 p + 2 n).
- β‑decay: neutron → proton + electron + antineutrino (or reverse for β⁺).
- γ‑decay: emission of high‑energy photon (no change in A or Z).
- Half‑life, t½: time for half the nuclei in a sample to decay. N = N₀ (½)^{t⁄t½}.
5.2 Fission & Fusion
- Fission: heavy nucleus splits into lighter fragments, releasing neutrons and large energy (e.g., ²³⁵U + n → ⁹⁴Kr + ¹⁴¹Ba + 3 n + ≈ 200 MeV).
- Fusion: light nuclei combine (e.g., ²H + ³H → ⁴He + n + ≈ 17 MeV). Requires very high temperature to overcome Coulomb barrier.
- Applications: nuclear power stations (controlled fission), medical isotopes, radiocarbon dating.
5.3 Radiation Protection (AO‑3)
- Shielding: α – paper; β – aluminium; γ – lead or concrete.
- Distance reduces dose by inverse‑square law.
- Time: minimise exposure.
6. Summary – Linking Observation to the Kinetic Particle Model
| Observation | Interpretation (kinetic model) |
|---|
| Microscopic particles jiggle in a still fluid. | Collisions with rapidly moving invisible molecules transfer momentum → random motion. |
| Jitteriness increases with temperature. | Higher temperature → greater average kinetic energy of molecules → more energetic collisions. |
| Motion is slower in viscous liquids. | Viscosity dampens the effect of molecular impacts, reducing net displacement. |
| Gas pressure rises when temperature rises (constant volume). | Faster molecules strike the container walls more often and with greater momentum. |
| Sound speed increases with temperature. | Particle vibration speed rises, allowing pressure disturbances to travel faster. |
7. Exam‑style Practice Questions
- Explain why the random motion of pollen grains in water provides evidence for the kinetic particle model.
- A student observes that Brownian motion becomes more vigorous when the water temperature is increased. Explain this using the kinetic model.
- Describe how the viscosity of a liquid influences the observed Brownian motion and why.
- Using the ideal‑gas equation, predict what happens to the pressure of a fixed mass of gas if its temperature is raised from 20 °C to 40 °C while the volume remains constant.
- Given D = k_B T ⁄ (6π η r), state how the mean‑square displacement changes if the particle radius is doubled, keeping all other factors constant.
- Calculate the work done when a 5 kg object is lifted 3 m vertically. State the energy store involved.
- A 12 V battery supplies a current of 2 A for 5 min. Determine the energy used in kWh.
- Sketch a distance‑time graph for an object moving with constant acceleration and label the gradient and area.
- State the three factors that affect the half‑life of a radioactive sample and give one practical application of each.
- Explain why sound cannot travel through a vacuum, referencing the particle model.
8. Quick Classroom Demonstrations
- Brownian Motion: Place a drop of milk in warm water, view under low‑power microscope, and ask students to describe how the jitteriness changes with temperature.
- Gas Pressure: Use a sealed syringe with a piston; heat the syringe and observe the piston move outward – discuss kinetic‑particle explanation.
- Wave Reflection: Shine a laser onto a mirror at an angle and measure the reflected angle to confirm the law of reflection.
- Magnetic Field: Sprinkle iron filings around a current‑carrying wire connected to a battery; the pattern shows the circular field lines.