General Physics
Motion, forces, energy, momentum, density, pressure and practical measurement.
IGCSE Physics
Structured chapter notes, diagrams and simulations prepared for focused IGCSE Physics revision.
Course map
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Motion, forces, energy, momentum, density, pressure and practical measurement.
Particle model, thermal properties, heat transfer and gas behaviour.
Wave properties, light, electromagnetic spectrum and sound.
Charge, circuits, safety, magnetism, induction, motors and transformers.
Atomic structure, radioactivity, emissions, half-life and safety.
Earth, Moon, solar system, stars, galaxies and universe expansion.
Chapter 1
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Chapter 2
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Chapter 3
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Chapter 4
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Chapter 6
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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.
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.
| 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 |
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.
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.
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.
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.
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.
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.
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.
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 explains atoms as mostly empty space with a tiny, dense, positively charged nucleus at the centre and electrons around it.
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.
Alpha particles were fired at thin gold foil and a detector measured how much they were deflected.
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 |
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.
Radioactivity covers background radiation, detection, alpha/beta/gamma emissions, radioactive decay, half-life and safe use of radioactive materials.
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.
Radiation is measured using a Geiger-Müller tube connected to a counter. The counter shows the count rate.
When measuring a source, background radiation must be subtracted from the measured count rate.
| 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 |
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 is a process where unstable atomic nuclei lose energy by emitting radiation.
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.
In balanced nuclear equations, the total mass number and total proton number are conserved.
Radioactive decay helps unstable nuclei become more stable by emitting alpha, beta or gamma radiation.
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.
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.
Ionising radiation can damage living cells. It can kill cells directly or cause mutations in DNA.
| 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. |
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.
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.