Radioactivity and Nuclear Physics

Ever wondered how nuclear power stations work or why we need to be careful around radioactive materials? Radioactivity is when unstable atoms emit radiation to become more stable, and it's happening all around us naturally.

A Geiger counter detects ionising radiation and measures the count rate in Becquerels (Bq). Even without any radioactive source nearby, you'll still detect background radiation from air (radon gas), rocks, soil, food, and even air travel.

There are two main risks when working with radioactive sources: irradiation (being exposed to radiation from a distance) and contamination (getting radioactive material on you). Radioactive decay is both random (you can't predict which atom will decay next) and spontaneous (external factors don't affect it).

Key Point: Always subtract background radiation from your readings to get the corrected count rate in experiments.

Atoms can have different numbers of neutrons whilst keeping the same number of protons - these are called isotopes. Unstable isotopes emit three types of radiation: alpha (helium nucleus with 2 protons and 2 neutrons), beta $high-speed electron$, and gamma (pure electromagnetic energy). Half-life is either the time for half the parent atoms to decay or for the activity to fall by half.

Nuclear fission powers nuclear stations by splitting large unstable nuclei $like Uranium-235$ into smaller, more stable ones, releasing energy and neutrons that cause a chain reaction. Nuclear fusion happens in stars, where small nuclei join to form larger ones, releasing the energy that makes stars shine.

Particle Model and States of Matter

Understanding how particles behave helps explain everything from why gases heat up when compressed to how your kettle boils water. The particle model shows that all matter consists of tiny particles in constant motion.

Internal energy of a system includes both the kinetic energy (movement) and potential energy of all particles. As temperature increases, particles move faster, so kinetic energy increases. You can calculate the change in kinetic energy using: change in kinetic energy = mass × specific heat capacity × change in temperature.

Density measures how tightly packed matter is in an object: density = mass ÷ volume. For regular shapes, measure dimensions and calculate volume. For irregular shapes, use a displacement method with water in a measuring cylinder to find volume.

Important: During state changes, temperature stays constant even though energy is still being added - this energy breaks or weakens bonds between particles.

When you compress a gas (like pumping up a tyre), you're doing work on it, which increases its temperature because particles gain energy and move faster. This explains why bike pumps get warm. Boyle's Law states that pressure is inversely proportional to volume - double the pressure and you halve the volume (if temperature stays constant).

Latent heat is the energy needed to change state without changing temperature. There's latent heat of fusion (solid to liquid) and latent heat of vaporisation (liquid to gas). Calculate this energy using: energy = mass × latent heat.

Electricity and Circuits

From your hair standing up near a Van de Graaff generator to powering your phone, electricity is all about the movement of electrons. Static electricity occurs when electrons transfer between materials through friction, creating positive and negative charges that attract or repel.

Current is the rate of flow of charge, measured in Amperes (A). Voltage is energy per unit charge, and resistance opposes current flow. Ohm's Law connects these: Voltage = Current × Resistance $V = IR$.

In series circuits, there's only one route for current, so current stays the same throughout but voltage splits across components. In parallel circuits, there are multiple routes, so voltage stays the same but current splits at junctions.

Circuit Tip: Series circuits - same current, voltage splits. Parallel circuits - same voltage, current splits.

The National Grid is the network of cables and transformers that delivers electricity from power stations to your home. Step-up transformers increase voltage for efficient long-distance transmission (higher voltage means lower current and less energy loss). Step-down transformers reduce voltage to safe levels for homes.

Safety features in mains electricity include the earth wire (0V, provides safe route for current if something goes wrong), neutral wire (0V, completes the circuit), and live wire (230V in UK, the dangerous one). The earth wire prevents you getting electrocuted if there's a fault.

Power stations generate electricity at around 25,000V, which gets stepped up to 400,000V for transmission, then stepped down through several stages to reach 230V in your home.

Energy Types and Transfers

Energy can't be created or destroyed, only transferred from one form to another - and you encounter these transfers constantly in daily life. The main types include kinetic (movement), potential (stored), thermal (heat), chemical (in fuels and food), and electrical (in circuits).

Energy efficiency compares useful energy output to total energy input: efficiency = (useful energy output ÷ total energy input) × 100%. Most energy transfers aren't 100% efficient - some energy always becomes waste heat. Car engines are only about 30% efficient, whilst LED bulbs can be over 90% efficient.

Heat transfers through three methods: conduction (through solids), convection (through liquids and gases), and radiation (electromagnetic waves that can travel through empty space). Understanding these helps explain everything from how radiators work to why space is cold.

Energy Formula: Kinetic energy = ½mv² and Gravitational potential energy = mgh

Power measures the rate of energy transfer: power = energy ÷ time or power = work done ÷ time. A 100W light bulb transfers 100 joules of energy every second. This helps you understand electricity bills and why some appliances cost more to run.

Renewable energy sources (wind, solar, hydroelectric) don't run out and produce less pollution, whilst non-renewable sources (fossil fuels, nuclear) will eventually run out but currently provide more reliable energy. Each has advantages and disadvantages in terms of cost, reliability, and environmental impact.

The specific heat capacity tells you how much energy is needed to raise 1kg of a substance by 1°C: energy = mass × specific heat capacity × temperature change. Water has a high specific heat capacity, which is why it takes ages to boil a kettle but also why hot water bottles stay warm for hours.