Know that thermal energy transfer by thermal radiation does not require a medium

1 Motion, Forces & Energy

Objective (Core)

Understand vectors, kinematics, Newton’s laws, work, energy, power and pressure.

Key Concepts

• Scalars & Vectors – magnitude only vs. magnitude + direction. Resultant of perpendicular vectors: R = √(A² + B²).
• Distance‑time & speed‑time graphs – gradient = speed/velocity, area under speed‑time graph = distance.
• Equations of motion (constant acceleration):
  • v = u + at
  • s = ut + ½at²
  • v² = u² + 2as
• Newton’s 2nd law: F = ma (net force = mass × acceleration).
• Momentum: p = mv; impulse = change in momentum = FΔt.
• Work, Energy & Power:
  • Work, W = F s cosθ (J)
  • Kinetic energy, Ek = ½mv²
  • Gravitational potential energy, Epg = mgh
  • Power, P = Work / time = Fv (W)
• Pressure: p = F / A (Pa). For fluids, p = ρgh.

Everyday Example

A car accelerating from rest: use v = u + at to find speed after 5 s if a = 2 m s⁻².

Common Misconceptions

• “Force and motion are the same.” – Force changes motion; motion can continue without a force (inertia).
• “Work is done whenever a force is applied.” – Work requires displacement in the direction of the force.

Quick Check

1. Calculate the work done when a 10 kg crate is pushed 3 m across a floor with a horizontal force of 50 N.
2. A pressure of 120 kPa acts on a piston of area 0.02 m². What is the force exerted?

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2 Thermal Physics

2.1 Particle Model of Matter (Core)

• Solids: particles vibrate about fixed positions.
• Liquids: particles close together but can move past each other.
• Gases: particles far apart, move freely, collisions are elastic.
• Temperature measures average kinetic energy of particles.

2.2 Thermal Expansion & Specific Heat (Core)

• Linear expansion: ΔL = α L₀ ΔT.
• Area expansion: ΔA = 2α A₀ ΔT.
• Volume expansion: ΔV = β V₀ ΔT (β ≈ 3α for solids).
• Specific heat capacity: Q = mcΔT.
• Latent heat: Q = mL (fusion or vaporisation).

2.3 Conduction & Convection (Core)

• Conduction – transfer of kinetic energy through direct particle collisions; occurs in solids, liquids, gases.
• Rate of heat transfer: Q/t = k A ΔT / d (k = thermal conductivity).
• Convection – bulk movement of fluid (liquid or gas) carrying heat; driven by density differences.
• Natural vs. forced convection (e.g., fans).

2.4 Radiation (Core)

Objective

Know that thermal energy transfer by thermal radiation does not require a material medium.

What is Thermal Radiation?

• All bodies with temperature > 0 K emit electromagnetic waves.
• Energy is carried by photons travelling at the speed of light, so radiation can pass through a vacuum.

Key Features

• Emitted by any surface with temperature T > 0 K.
• No material medium is needed – radiation can cross empty space.
• Amount emitted depends on:
  • Temperature of the surface,
  • Surface area,
  • Emissivity (colour/texture),
  • Distance from the source (inverse‑square law).

Electromagnetic Spectrum

Thermal radiation is strongest in the infrared region; as temperature rises the peak shifts toward visible light and ultraviolet. All electromagnetic waves travel at

\(c = 3.0 \times 10^{8}\ \text{m s}^{-1}\) in vacuum.

Black‑Body Radiation

A *perfect black body* absorbs all incident radiation and re‑emits the maximum possible amount for its temperature. Real objects have an emissivity e (0 < e ≤ 1).

Colour / texture and emissivity – a black, matte surface has a high emissivity (≈ 1); a shiny metal has a low emissivity (≈ 0.1). Darker, rougher surfaces radiate more efficiently.

Stefan‑Boltzmann Law

The total power radiated by a surface of area A is

\(P = \sigma \, e \, A \, T^{4}\)

• \(\sigma = 5.67 \times 10^{-8}\ \text{W m}^{-2}\text{K}^{-4}\) (Stefan‑Boltzmann constant)
• e = emissivity
• T = absolute temperature (K)

Factors Affecting the Amount of Radiation

1. Temperature – radiation ∝ T⁴ (Stefan‑Boltzmann).
2. Surface area – larger area radiates more (direct proportion).
3. Emissivity – high‑e surfaces emit more than low‑e surfaces.
4. Distance – intensity falls as 1 / r² (inverse‑square law).

Simple Classroom Demonstration

1. Place a heated metal plate (~150 °C) inside a clear vacuum jar.
2. Position a second, initially cool aluminium plate 5 cm away.
3. Seal the jar, evacuate the air with a hand pump, and record the temperature rise of the cool plate.
4. Repeat with the jar filled with air. The plate heats faster with air (conduction + convection) and slower in vacuum (radiation only), showing that radiation works without a medium.

Comparison with Conduction and Convection

Aspect	Conduction	Convection	Radiation
Medium required	Yes – solid or liquid	Yes – fluid (liquid or gas)	No – can occur in vacuum
Mechanism	Kinetic energy transfer between adjacent particles	Bulk movement of fluid carrying energy	Emission of electromagnetic waves (photons)
Dependence on temperature	∝ temperature gradient	∝ temperature difference & fluid motion	∝ T⁴ (Stefan‑Boltzmann)

Everyday Applications & Consequences

• Sunlight reaching Earth – the only way solar energy travels through space.
• Heat loss from house walls and windows at night.
• Cup of tea cooling to surrounding air.
• Astronaut thermal blankets – low‑emissivity surfaces minimise radiation loss.

Common Misconceptions

• “Radiation needs air.” – False. Radiation can cross empty space; conduction and convection need a material medium.
• “All radiation is harmful.” – False. Thermal radiation is a normal, everyday form of heat transfer.

Quick Check Questions

1. Explain why the Moon, which has no atmosphere, still gets warm during the day.
2. Two objects have the same temperature but different colours (black vs. shiny metal). Which emits more radiation and why?
3. Calculate the power radiated by a black‑body sphere of radius 0.05 m at 300 K. (Use e = 1.)

Summary

Thermal radiation transfers heat without any material medium. It depends strongly on temperature, surface area, emissivity and distance, and is the only way heat can travel across the vacuum of space.

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3 Waves

Objective (Core)

Describe the properties of mechanical and electromagnetic waves, and apply the wave‑speed relationship.

Key Concepts

• Wave definition – a disturbance that transfers energy without permanent displacement of matter.
• Types:
  • Mechanical waves (require a medium) – transverse & longitudinal.
  • Electromagnetic (EM) waves – do not require a medium.
• Wave speed: \(v = f\lambda\) (v = speed, f = frequency, λ = wavelength).
• Reflection & refraction – angle of incidence = angle of reflection; Snell’s law for refraction.
• Diffraction – bending of waves around obstacles; noticeable when obstacle size ≈ λ.
• Superposition & interference – constructive (bright) and destructive (dark) patterns.

Light as an EM Wave

• Visible spectrum: 400 nm – 700 nm.
• Reflection from mirrors, refraction in lenses, dispersion in prisms.
• Speed in vacuum: \(c = 3.0 \times 10^{8}\ \text{m s}^{-1}\); in a medium \(v = c/n\) (n = refractive index).

Everyday Example

A radio station broadcasts at 100 MHz. The wavelength is λ = c/f ≈ 3 m.

Common Misconceptions

• “Sound can travel in space.” – False; sound is a mechanical wave and needs a material medium.
• “All waves travel at the same speed.” – Speed depends on the medium and wave type.

Quick Check

1. Find the frequency of a wave with λ = 0.5 m travelling at 340 m s⁻¹ (speed of sound).
2. A ray of light passes from air (n≈1.0) into water (n≈1.33). If the angle of incidence is 30°, calculate the angle of refraction.

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4 Electricity & Magnetism

4.1 Electrostatics (Core)

• Charge: two types, + and –; like charges repel, unlike attract.
• Conservation of charge.
• Electric field (E) – direction of force on a positive test charge; magnitude = F/q.
• Conductors vs. insulators.
• Charging by friction, conduction and induction.

4.2 Current, Voltage & Resistance (Core)

• Current, I = Q/t (A).
• Potential difference, V = W/Q (V).
• Resistance, R = V/I (Ω). Ohm’s law: V = IR.
• Power, P = VI = I²R = V²/R (W).
• Resistivity, ρ: R = ρ L / A.

4.3 Series & Parallel Circuits (Core)

• Series: same current, total resistance Rₜ = ΣR.
• Parallel: same voltage, 1/Rₜ = Σ(1/R).
• Use a multimeter to measure V, I and R safely.

4.4 Magnetism (Core)

• Magnetic field lines emerge from north pole, enter south pole.
• Force on a moving charge: \(F = qvB\sin\theta\).
• Force on a current‑carrying conductor: \(F = BIL\sin\theta\).
• Earth’s magnetic field ≈ 5 × 10⁻⁵ T.

4.5 Electromagnetic Induction (Core)

• Faraday’s law: induced emf ∝ rate of change of magnetic flux.
• Direction given by Lenz’s law (opposes change).
• Generators convert mechanical energy to electrical; transformers change voltage levels.

Everyday Applications

• Household wiring (series/parallel, safety fuses).
• Electric motors in fans and toys – interaction of current and magnetic field.
• Induction cooktops – heating by rapidly changing magnetic fields.

Common Misconceptions

• “Current is ‘used up’ by a device.” – Current is the same at all points in a series circuit; devices convert electrical energy, not current.
• “A magnet only has a north pole.” – Every magnet has both north and south poles; cutting a magnet creates two new dipoles.

Quick Check

1. Calculate the resistance of a copper wire 2 m long, cross‑sectional area 1 mm² (ρ = 1.7 × 10⁻⁸ Ω m).
2. A coil of 50 turns, area 0.01 m², rotates at 60 rev s⁻¹ in a 0.2 T magnetic field. Find the peak emf.

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5 Nuclear Physics

Objective (Core)

Explain the structure of the atom, types of radiation, and concepts of half‑life and nuclear stability.

Key Concepts

• Atomic structure – nucleus (protons + neutrons) surrounded by electrons.
• Isotopes: same Z (protons) different N (neutrons).
• Radioactive decay:
  • α‑decay: emission of a helium nucleus (2p + 2n); mass ↓4, Z ↓2.
  • β‑decay: neutron → proton + electron + antineutrino; Z ↑1.
  • γ‑decay: emission of high‑energy photons; no change in Z or A.
• Half‑life (t½) – time for half the nuclei in a sample to decay. Activity A = λN, where λ = ln2 / t½.
• Applications: medical imaging (X‑rays, PET), power (nuclear reactors), carbon‑14 dating.
• Safety: shielding (α – paper, β – aluminium, γ – lead), distance and time.

Example Calculation

If a 5 g sample of a radionuclide with t½ = 30 min contains 2 × 10¹⁸ atoms initially, how many atoms remain after 90 min?

Common Misconceptions

• “Radiation always means harmful.” – Low‑dose radiation is used safely in medicine.
• “All radioactive materials are dangerous.” – Some have short half‑lives and decay to stable, harmless products.

Quick Check

1. Write the nuclear equation for the β‑decay of carbon‑14.
2. Calculate the activity (in becquerels) of a sample containing 1 × 10⁶ decays per second.

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6 Space Physics

Objective (Core)

Understand Earth’s rotation and orbit, the cause of seasons, lunar phases and basic solar system structure.

Key Points

• Earth’s rotation – 24 h period; causes day/night.
• Earth’s orbit – nearly circular, 365.25 d; speed ≈ 30 km s⁻¹.
• Seasons – result from axial tilt (≈ 23.5°) causing varying solar angle and day length.
• Lunar phases – geometry of Sun‑Earth‑Moon system; full moon when Earth is between Sun and Moon.
• Eclipses – solar (Moon blocks Sun) and lunar (Earth blocks Sun’s light).
• Solar system hierarchy: Sun → planets → moons → dwarf planets, asteroids, comets.

Everyday Example

Why are the days longer in summer for the Northern Hemisphere? – Higher solar elevation and longer daylight due to tilt.

Common Misconceptions

• “Seasons are caused by Earth’s distance from the Sun.” – Distance variation is small; tilt is the dominant factor.
• “The Moon produces its own light.” – Moon reflects sunlight.

Quick Check

1. Sketch the Earth’s position in its orbit when the Northern Hemisphere experiences summer solstice.
2. Explain why a total solar eclipse can be seen from only a narrow strip on Earth.

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7 Practical Skills (Core)

Checklist of Required Experiments

Skill	Typical Experiment	Key Measurements / Equipment
Measuring density	Solid density using mass and volume (water‑displacement)	Balance, graduated cylinder, ruler
Investigating Hooke’s law	Force vs. extension of a spring	Force sensor or spring balance, metre rule
Heat capacity	Specific heat of water (calorimetry)	Thermometer, calorimeter, electric heater
Radiation measurement	Thermopile or infrared sensor to detect heat from a heated plate	Thermopile, voltmeter, vacuum jar (optional)
Wave properties	Ripple tank – wavelength, speed, refraction	Ripple tank, ruler, stopwatch
Circuit analysis	Series & parallel resistor networks, use of multimeter	Breadboard, resistors, ammeter, voltmeter
Magnetic field mapping	Compass deflection around a bar magnet	Compass, ruler, magnet
Radioactivity (safety‑approved)	Background radiation measurement with a Geiger‑Müller tube	GM counter, shielding materials

Safety Reminders

• Always wear safety goggles and follow the teacher’s instructions.
• Handle hot objects with tongs; allow cooling before touching.
• Use low‑voltage circuits (≤ 12 V) unless supervised.
• For radiation work, use approved sources and appropriate shielding.

Data Handling Tips

• Record raw data in a table, include units.
• Calculate uncertainties (±) and propagate them where required.
• Plot graphs with labelled axes, straight‑line fits where theory predicts linearity.
• Interpret slope/intercept in terms of physical constants (e.g., gradient = g in a free‑fall experiment).

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Summary of Core Content

This set of notes covers all six core blocks of the Cambridge IGCSE Physics syllabus:

• Motion, forces & energy – vectors, kinematics, Newton’s laws, work, power and pressure.
• Thermal physics – particle model, expansion, specific heat, conduction, convection and radiation (including the Stefan‑Boltzmann law and the fact that radiation needs no medium).
• Waves – mechanical & electromagnetic waves, speed, reflection, refraction, diffraction and interference.
• Electricity & magnetism – electrostatics, circuits, magnetism, electromagnetic induction.
• Nuclear physics – atomic structure, types of decay, half‑life and applications.
• Space physics – Earth’s rotation & orbit, seasons, lunar phases and basic solar‑system layout.

Practical skills essential for Paper 5/6 are listed with typical experiments, safety advice and data‑handling guidelines. Mastery of these concepts, equations and experimental techniques will provide a solid foundation for the IGCSE examinations.