Nuclear Radiation Basics

Think about atoms as tiny building blocks that aren't always stable - when they break down, they release nuclear radiation. This happens when unstable nuclei decay by emitting different types of particles to become more stable.

There are four main types of radiation you need to know. Alpha particles consist of 2 protons and 2 neutrons, reducing both the mass number by 4 and atomic number by 2. Beta particles are high-speed electrons formed when a neutron turns into a proton, with virtually no mass but a negative charge.

Gamma rays don't change the nucleus at all - they're just excess energy being released. Neutron emission only reduces the mass number by 1 whilst keeping the atomic number the same.

Key Point: Each type of radiation has different penetrating power - alpha is stopped by skin/paper, beta by aluminium, and gamma requires thick lead to block it effectively.

Half-Life and Nuclear Equations

Here's something that might surprise you - radioactive decay is completely random, meaning scientists can't predict exactly when a specific nucleus will decay. However, they can use statistics to predict patterns for large groups of nuclei.

Half-life is the time it takes for half the unstable nuclei in a sample to decay (or for the count rate to halve). You can spot this on graphs by finding where the activity drops to half its original value - it's a powerful tool for dating materials and medical applications.

For calculations, you'll need to work out how much material remains after several half-lives. If you start with 120 Bq and the half-life is 1.5 days, after 3 days you'd have 120 → 60 → 30 Bq.

Key Point: Nuclear equations must balance - the mass numbers and atomic numbers on both sides must add up correctly.

Work, Power and Energy Transfer

Energy is constantly moving around us, and work done is simply energy being transferred from one form to another. When you push something and it moves, you're doing work - calculated as force × distance.

Power tells you how quickly energy is being transferred (work done ÷ time). Think of it like the difference between walking and running up stairs - you do the same work, but running requires more power.

Energy transfers through three main methods. Conduction happens in solids when vibrating particles pass energy to neighbours. Convection occurs in fluids when hot material rises and cold material sinks. Radiation doesn't need particles at all - like heat from the Sun reaching Earth.

Specific heat capacity is the energy needed to raise 1kg of material by 1°C. Materials with high specific heat capacity (like water) take lots of energy to heat up, which is why coastal areas have milder temperatures.

Key Point: Energy is always conserved - it can't be created or destroyed, only transferred between different forms and stores.

Energy Resources and Sustainability

Energy resources split into two crucial categories that'll definitely appear in your exams. Renewable resources like wind, solar, and hydroelectricity replenish themselves naturally, whilst non-renewable resources like fossil fuels and nuclear fuel have finite amounts.

Each energy source comes with trade-offs you need to understand. Fossil fuels release CO₂ contributing to climate change, whilst nuclear power creates radioactive waste but produces no greenhouse gases during operation. Wind and solar are clean but require large areas and don't work consistently.

Carbon neutral energy sources either produce no CO₂ or absorb as much as they release. Biomass can be carbon neutral because plants absorb CO₂ as they grow, balancing out emissions when burned.

The choice of energy resources depends on local factors - sunny countries favour solar, windy coastlines suit wind farms, and mountainous regions often use hydroelectricity.

Key Point: There's no perfect energy source - each involves compromises between environmental impact, cost, reliability, and availability.

Electric Circuits and Current

Electric current is simply the flow of electrons through a conductor, measured in amperes (A). You'll encounter direct current (DC) from batteries that flows in one direction, and alternating current (AC) from mains electricity that regularly changes direction.

Understanding circuit symbols is essential - you'll need to recognise switches, lamps, resistors, voltmeters, ammeters, and specialized components like LEDs and diodes. These symbols are your language for drawing and interpreting circuit diagrams.

Resistance opposes the flow of current, whilst potential difference (voltage) provides the driving force that pushes electrons around the circuit. Think of it like water flowing through pipes - voltage is the pressure and resistance is anything that restricts the flow.

Key Point: Charge = current × time, and this relationship helps you calculate how much electrical charge flows through any component over a given period.

Series and Parallel Circuits

Series circuits connect components one after another like fairy lights - if one breaks, they all stop working. Current stays the same throughout $I₁ = I₂ = I₃$, but voltage splits between components, and total resistance adds up $R_total = R₁ + R₂$.

Parallel circuits offer multiple paths for current, like lanes on a motorway. If one component fails, others keep working. Current splits at junctions $I_total = I₁ + I₂$, but voltage stays the same across each branch.

When electrons flow through wires, they collide with atoms and transfer energy as heat - this is why electrical devices warm up. This isn't always wasteful though - it's exactly how electric heaters and kettles work.

Power calculations are crucial: Power = current × voltage $P = IV$ or Power = current² × resistance $P = I²R$. These help you work out energy consumption and running costs.

Key Point: Parallel circuits are more practical for homes because each appliance gets full mains voltage and works independently.

Special Circuit Components

Some components have variable resistance that changes with conditions, making them perfect for sensors and control systems. Understanding these will help you tackle exam questions about automatic devices.

Thermistors change resistance with temperature - as temperature increases, resistance typically decreases. You'll find these in car engines, fire alarms, and heating systems where automatic temperature control is needed.

Light Dependent Resistors (LDRs) have high resistance in darkness and low resistance in bright light. They're used in automatic street lighting, camera exposure systems, and security lights that switch on at dusk.

Diodes are one-way valves for electricity, only allowing current to flow in one direction. They're essential for converting AC to DC and protecting sensitive electronic components from damage.

Key Point: These components are called "sensors" because their changing resistance allows circuits to respond automatically to environmental changes.