IGCSE Physics
Interactive Study Notes
Structured chapter notes, diagrams and simulations prepared for focused IGCSE Physics revision.
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General Physics
Motion, forces, energy, momentum, density, pressure and practical measurement.
Thermal Physics
Particle model, thermal properties, heat transfer and gas behaviour.
Waves
Wave properties, light, electromagnetic spectrum and sound.
Electricity and Magnetism
Charge, circuits, safety, magnetism, induction, motors and transformers.
Nuclear Physics
Atomic structure, radioactivity, emissions, half-life and safety.
Space Physics
Earth, Moon, solar system, stars, galaxies and universe expansion.
Chapter 1
General Physics
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Chapter 2
Thermal Physics
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Chapter 3
Waves
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Chapter 4
Electricity and Magnetism
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Chapter 5
Nuclear Physics
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Chapter 6
Space Physics
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Motion, Forces and Energy Overview
Chapter Focus
This chapter builds the core mechanics ideas used throughout IGCSE Physics. You start by describing motion accurately, then connect motion to forces, momentum, energy, work and pressure.
Speed, velocity, acceleration, distance-time graphs and speed-time graphs.
Weight, resultant forces, moments, stretching, turning effects and conservation of momentum.
Work, power, energy stores, density and pressure in solids, liquids and gases.
Definition
Motion
Speed, Velocity and Acceleration
Speed is the distance travelled per unit time. Velocity is speed in a specified direction, so it is a vector quantity.
On a distance-time graph, the gradient gives speed. On a speed-time graph, the area underneath gives distance travelled.
Graph Shapes
| Motion | Distance-time graph | Speed-time graph |
|---|---|---|
| At rest | Horizontal line | Line on the time axis |
| Constant speed | Straight sloping line | Horizontal line above the axis |
| Accelerating | Curve with increasing gradient | Upward sloping line |
| Decelerating | Curve with decreasing gradient | Downward sloping line |
Terminal Velocity
In air, falling objects do not keep accelerating forever. As speed increases, air resistance increases until it balances weight. The object then falls at constant speed called terminal velocity.
Terminal Velocity
Density
Density Equation
Density is mass per unit volume. It tells us how much matter is packed into a given volume.
Common units are kg/m3 and g/cm3.
Measuring Density
Measure the mass of the empty container, add a known volume of liquid, then subtract to find the liquid mass.
Measure mass with a balance and calculate volume using length × width × height.
Use water displacement to find volume, then calculate density.
Floating and Sinking
An object floats if its density is less than the density of the liquid. It sinks if its density is greater than the liquid density.
Density and Floating
Thermal Physics Overview
What This Chapter Covers
Thermal physics explains matter using particles, then connects temperature, internal energy, expansion, heat capacity, latent heat and thermal energy transfer.
Solids, liquids and gases are explained by particle arrangement, motion and forces.
Temperature, expansion, heat capacity, latent heat and gas pressure.
Conduction, convection and radiation explain how energy moves between objects.
Core Equations
Waves Overview
What This Chapter Covers
Waves transfer energy without transferring matter. This chapter links wave properties to light, the electromagnetic spectrum and sound.
Amplitude, wavelength, frequency, period, speed, reflection, refraction and diffraction.
Reflection, refraction, lenses, total internal reflection and ray diagrams.
Uses, dangers, transverse electromagnetic waves and longitudinal sound waves.
Core Equation
Electricity and Magnetism Overview
What This Chapter Covers
This chapter moves from charges and circuits to practical electrical safety, then into magnetic fields, induction, motors, generators and transformers.
Charge, current, potential difference, resistance, electrical energy and power.
Series and parallel circuits, circuit symbols, components and their uses.
Magnetic fields, induction, generators, motors and transformers.
Core Equations
Nuclear Physics Overview
What This Chapter Covers
Nuclear physics studies the structure of atoms, the nucleus, radioactivity, radioactive decay, half-life and safe handling of ionising radiation.
Atoms, nuclei, protons, neutrons, electrons, isotopes, fission and fusion.
Background radiation, nuclear emissions, decay, half-life and safety precautions.
The nuclear model of the atom
Topic Map
The nuclear model explains atoms as mostly empty space with a tiny, dense, positively charged nucleus at the centre and electrons around it.
- 5.1.1 The atom: atomic structure, ions and Rutherford alpha scattering.
- 5.1.2 The nucleus: protons, neutrons, isotopes, fission, fusion and mass-energy equivalence.
The atom
Structure of an Atom
- An atom has a positively charged nucleus containing protons and neutrons.
- Negatively charged electrons orbit the nucleus in energy levels or shells.
- The nucleus is tiny compared with the atom but contains most of the atom’s mass.
- The atom is mostly empty space between the nucleus and the electrons.
Formation of Ions
Positive ions form when atoms lose electrons. Negative ions form when atoms gain electrons.
Ions are charged because the number of protons is not equal to the number of electrons.
Rutherford Alpha Scattering
Alpha particles were fired at thin gold foil and a detector measured how much they were deflected.
- Most alpha particles passed straight through, showing atoms are mostly empty space.
- A few were slightly deflected, showing the atom contains a tiny concentrated mass.
- Very few bounced back, showing the nucleus is positively charged and repels alpha particles.
Scale of the Atom
The nucleus
Composition of the Nucleus
The nucleus contains protons and neutrons. Electrons orbit outside the nucleus and have negligible mass compared with protons and neutrons.
| Particle | Position | Relative charge | Relative mass |
|---|---|---|---|
| Proton | In nucleus | +1 | 1 |
| Neutron | In nucleus | 0 | 1 |
| Electron | Orbiting nucleus | -1 | ~0 |
Proton Number and Nucleon Number
- Proton number, Z, is the number of protons and defines the element.
- Nucleon number, A, is the total number of protons and neutrons.
- Neutron number is found using N = A – Z.
Isotopes
Isotopes are atoms of the same element with the same proton number but different neutron numbers.
Hydrogen isotopes have the same charge because they all have one proton, but different masses because they have different numbers of neutrons.
Fission, Fusion and E = mc²
- Fission is the splitting of a heavy nucleus, such as uranium-235, releasing energy and neutrons.
- Fusion is the joining of light nuclei at very high temperatures, as in stars.
- A small loss of mass can release a large amount of energy because E = mc².
Radioactivity
Topic Map
Radioactivity covers background radiation, detection, alpha/beta/gamma emissions, radioactive decay, half-life and safe use of radioactive materials.
- 5.2.1 Detection of radioactivity
- 5.2.2 The three types of nuclear emission
- 5.2.3 Radioactive decay
- 5.2.4 Half-life
- 5.2.5 Safety precautions
Detection of radioactivity
Background Radiation
Background radiation is the low level of radiation that is always present in our surroundings. It comes from natural and artificial sources.
Radon gas, rocks, buildings, food, drink and cosmic rays.
Medical use, nuclear industry, past weapons testing and flying.
Measuring Radiation
Radiation is measured using a Geiger-Müller tube connected to a counter. The counter shows the count rate.
Corrected Count Rate
When measuring a source, background radiation must be subtracted from the measured count rate.
The three types of nuclear emission
Alpha, Beta and Gamma
| Emission | Nature | Charge | Penetration | Ionising effect |
|---|---|---|---|---|
| Alpha | Helium nucleus | +2 | Stopped by paper/skin | Very strong |
| Beta minus | High-speed electron | -1 | Stopped by aluminium | Moderate |
| Gamma | Electromagnetic wave | 0 | Reduced by lead/concrete | Very weak |
Deflection in Fields
- Alpha and beta particles are charged, so they are deflected by electric and magnetic fields.
- Alpha particles are positive and beta minus particles are negative, so they deflect in opposite directions.
- Beta particles deflect more because they are much lighter.
- Gamma rays are uncharged, so they are not deflected.
Ionisation and Penetration
Alpha particles have strong ionising power but low penetration. Gamma rays have weak ionising power but high penetration because they interact much less with matter.
Radioactive decay
Radioactive Decay
Radioactive decay is a process where unstable atomic nuclei lose energy by emitting radiation.
- It is spontaneous, so it happens without external influence.
- It is random, so we cannot predict exactly when a particular nucleus will decay.
- Temperature and pressure do not affect radioactive decay.
Types of Emission
The nucleus loses 2 protons and 2 neutrons. Atomic number decreases by 2 and mass number decreases by 4.
A neutron changes into a proton and an electron. Atomic number increases by 1 and mass number stays the same.
The nucleus releases energy. Atomic number and mass number do not change.
Decay Equation Patterns
In balanced nuclear equations, the total mass number and total proton number are conserved.
Summary
Radioactive decay helps unstable nuclei become more stable by emitting alpha, beta or gamma radiation.
Half-life
Definition of Half-Life
Half-life is the time taken for half the nuclei in a radioactive sample to decay.
It is also the time taken for the activity or count rate of a radioactive source to reduce to half.
- Half-life is constant for a given isotope.
- Half-life is independent of the initial amount of radioactive material.
Example Calculation
A sample has a count rate of 800 Bq. If the half-life is 5 years, what is the count rate after 15 years?
Final count rate = 100 Bq.
Half-life Decay
Safety precautions
Effects of Ionising Nuclear Radiation
Ionising radiation can damage living cells. It can kill cells directly or cause mutations in DNA.
- DNA mutations may lead to uncontrolled cell division and cancer.
- Mutations in reproductive cells may lead to birth defects.
- Even small doses over a long period can be harmful if exposure is not monitored.
Safe Handling and Storage
| Precaution | Purpose |
|---|---|
| Protective suits | Reduce radiation exposure, especially when stronger sources are used. |
| Hazard labels | Warn people to keep distance and limit exposure time. |
| Dosimeter badges | Monitor the radiation dose received by workers. |
| Remote handling | Allows sources to be handled from a safer distance or behind shielding. |
| Lead-lined storage | Absorbs radiation when sources are not in use. |
Key Safety Principles
Less time near the source means a lower dose.
Radiation intensity decreases as distance increases.
Use paper for alpha, aluminium for beta, and lead or concrete for gamma.
Quick Recap
Space Physics Overview
What This Chapter Covers
Space physics connects Earth, the Moon, the Solar System, stars, galaxies and the expanding Universe.
Day and night, seasons, orbits, phases and eclipses.
Planets, dwarf planets, comets, moons and orbital motion under gravity.
Stellar life cycles, galaxies, redshift and evidence for expansion.
Key Ideas
- Gravity provides the centripetal force needed for orbital motion.
- The Sun is a star and produces energy by nuclear fusion.
- Redshift from distant galaxies is evidence that the Universe is expanding.