Cambridge IGCSE Physics (0625) – Core Notes
1. Motion, Forces & Energy
- Scalars and vectors – speed, distance (scalar); velocity, displacement (vector).
- Equations of motion (constant acceleration)
- v = u + at
- s = ut + ½at²
- v² = u² + 2as
- Graphs – interpreting gradient (speed/acceleration) and area (displacement).
- Newton’s Laws
- 1st law – inertia.
- 2nd law – F = ma.
- 3rd law – action–reaction.
- Momentum and impulse – p = mv; impulse = FΔt = Δp.
- Work, energy and power
- Work = F · s (J).
- Kinetic energy = ½mv², gravitational PE = mgh.
- Power = work / time = Fv = ΔE / Δt.
- Pressure, density and simple machines
- Pressure = F/A (Pa).
- Density = m/V (kg m⁻³).
- Mechanical advantage of levers, pulleys, inclined planes.
2. Thermal Physics
- Particle model of matter – particles vibrate; temperature measures average kinetic energy.
- Specific heat capacity – Q = mcΔT.
- Phase changes
- Latent heat of fusion/melting and vaporisation/condensation.
- Q = mL (L = latent heat).
- Modes of heat transfer
- Conduction – through solids, proportional to ΔT and area, inversely to length.
- Convection – fluid motion, driven by density differences.
- Radiation – electromagnetic waves; obeys Stefan‑Boltzmann law (P ∝ T⁴).
- Thermal expansion – linear ΔL = αL₀ΔT; volumetric ΔV = βV₀ΔT.
3. Waves
- Wave terminology – crest, trough, wavelength (λ), frequency (f), period (T), speed (v = fλ).
- Types of waves
- Transverse – displacement ⟂ to direction of travel (e.g., light, water surface).
- Longitudinal – displacement ‖ to direction of travel (e.g., sound).
- Reflection, refraction & diffraction – basic laws and everyday examples.
- Standing waves & resonance – nodes, antinodes; musical instruments, microwave ovens.
3.1 Electromagnetic (EM) Spectrum
| Region | Frequency (Hz) | Wavelength (m) | Typical uses (IGCSE) |
|---|
| Radio | 3 × 10³ – 3 × 10⁹ | 10⁵ – 0.1 | Broadcasting, RFID, navigation, low‑orbit satellite phones |
| Microwave | 3 × 10⁹ – 3 × 10¹¹ | 0.1 – 1 × 10⁻³ | Satellite communication, radar, microwave ovens, DBS TV, Wi‑Fi (2.4 GHz) |
| Infrared (IR) | 3 × 10¹¹ – 4 × 10¹⁴ | 1 × 10⁻³ – 7 × 10⁻⁷ | Remote controls, thermal imaging, heating |
| Visible | 4 × 10¹⁴ – 7.5 × 10¹⁴ | 7 × 10⁻⁷ – 4 × 10⁻⁷ | Human vision, photography, LEDs |
| Ultraviolet (UV) | 7.5 × 10¹⁴ – 3 × 10¹⁶ | 4 × 10⁻⁷ – 1 × 10⁻⁸ | Disinfection, sun‑cream testing, fluorescence |
| X‑ray | 3 × 10¹⁶ – 3 × 10¹⁹ | 1 × 10⁻⁸ – 1 × 10⁻¹¹ | Medical imaging, security scanners |
| Gamma‑ray (γ‑ray) | > 3 × 10¹⁹ | < 1 × 10⁻¹¹ | Cancer treatment, food sterilisation, astrophysics |
3.2 Why Microwaves Are Used for Satellite Links
- Low atmospheric attenuation in “microwave windows” (≈ 2 GHz, 8 GHz, 12 GHz).
- Shorter wavelengths → modest antenna sizes with high directivity.
- Ability to carry large bandwidths → high data rates.
- Microwaves are non‑ionising, so health risks are limited to heating at very high powers.
4. Electricity & Magnetism
- Charge, current and potential difference
- Current I = ΔQ / Δt (A).
- Potential difference V = W / Q (V).
- Resistance and Ohm’s law – R = V/I; resistivity ρ, R = ρ ℓ / A.
- Power in electrical circuits – P = VI = I²R = V²/R.
- Series and parallel circuits – rules for total resistance, voltage division, current division.
- Magnetic fields
- Field lines, Earth’s field, right‑hand rule for current‑carrying conductors.
- Force on a conductor: F = BIL sinθ.
- Electromagnetic induction
- Faraday’s law – induced emf ∝ rate of change of magnetic flux.
- Lenz’s law – direction opposes the change.
- Applications: generators, transformers, induction cookers.
- Transformers – step‑up and step‑down; V₁/V₂ = N₁/N₂, I₁/I₂ = N₂/N₁ (ideal).
5. Nuclear Physics
- Structure of the atom – nucleus (protons, neutrons) + electrons.
- Isotopes – same Z, different A; stability and natural abundance.
- Radioactive decay
- α‑decay (He‑2 nucleus), β‑decay (electron or positron), γ‑decay (photon).
- Half‑life (t½) – exponential decay law N = N₀(½)^{t/t½}.
- Fission and fusion
- Fission – heavy nucleus splits, releases neutrons and energy (e.g., ²³⁵U).
- Fusion – light nuclei combine (e.g., ²H + ³H → ⁴He), powers the Sun.
- Applications & safety
- Medical imaging (PET, radiotherapy), power generation, smoke detectors.
- Shielding (lead, concrete), ALARA principle, dosimetry.
6. Space Physics
6.1 Orbital Mechanics Basics
- Kepler’s 1st law – planets (and satellites) move in ellipses with Earth at a focus.
- Kepler’s 2nd law – line joining satellite to Earth sweeps equal areas in equal times (conservation of angular momentum).
- Kepler’s 3rd law (simplified for circular orbits) – T² ∝ r³, where T = orbital period, r = orbital radius.
- Geostationary orbit (GEO)
- Altitude ≈ 35 786 km, period = 24 h, zero inclination → satellite appears stationary over the equator.
- Large footprint: one satellite covers ~⅓ of Earth’s surface.
- Low‑Earth orbit (LEO)
- Altitude 500–2 000 km, period ≈ 90–120 min.
- Small footprint → many satellites needed for continuous coverage.
6.2 Satellite Communication Using Microwaves
| Feature | LEO Satellite Phones | GEO Satellite TV & Phone Services |
|---|
| Typical altitude (km) | 500 – 2 000 | ≈ 35 786 |
| Orbital period | 90–120 min | 24 h (synchronous) |
| Microwave band used | L‑band (1.5–2.5 GHz) or S‑band (2.4–2.5 GHz) | Ku‑band (12–14 GHz) for TV; L‑band for some phones |
| Signal latency (one‑way) | ≈ 5–10 ms | ≈ 125–150 ms |
| Coverage per satellite | Small – requires a constellation (e.g., Iridium, Globalstar) | Very large – three GEO satellites give near‑global service |
| Typical applications | Mobile voice, low‑latency broadband, IoT, Earth observation | Direct‑broadcast TV, some satellite phones, broadband internet (e.g., VSAT) |
6.3 Practical Aspects of Satellite Links
- Antenna design – parabolic dish for GEO (high gain, narrow beam); phased‑array or patch antenna for handheld LEO phones.
- Link budget – transmitter power, antenna gains, free‑space path loss (FSPL = 20 log₁₀(d) + 20 log₁₀(f) + 92.45, d in km, f in GHz), receiver sensitivity.
- Digital signalling – modulation (QPSK, 8‑PSK), error‑correction codes, benefits: higher data rates, noise tolerance, easy regeneration.
- Health & safety – microwave exposure limits (ICNIRP), only high‑power transmitters (e.g., radar) pose a risk; satellite phones operate at low power.
7. Practical / Experimental Skills (Cross‑Topic)
- Using stop‑watches and motion sensors to obtain acceleration graphs.
- Measuring resistance with a multimeter; constructing series/parallel circuits on a breadboard.
- Determining specific heat capacity by calorimetry (water‑mixing method).
- Investigating wave properties with ripple tanks and string‑wave setups (measure λ, f, v).
- Mapping magnetic field lines with iron filings or a Hall probe.
- Radioactive decay experiments – background counts, half‑life determination using a Geiger‑Müller tube (subject to safety rules).
- Simple satellite‑link demonstration: transmitting a low‑power microwave signal to a dish and detecting it with a receiver module (illustrates line‑of‑sight and antenna gain).
8. Summary
Microwaves sit in the middle of the electromagnetic spectrum and are the preferred carrier for satellite communication because they suffer little atmospheric loss and can be directed with reasonably sized antennas. Low‑orbit satellites provide low latency and are ideal for mobile voice and broadband services, while geostationary satellites give wide‑area coverage suitable for direct‑broadcast television and some satellite‑phone networks. Understanding the underlying physics – from wave behaviour and EM theory to orbital mechanics, digital signalling, and safety – equips students to answer the full range of IGCSE questions across the six core syllabus blocks.