Energy Resources and Transfers

Energy stores are like different ways energy can be "kept" - think kinetic energy in moving objects, gravitational potential energy in anything up high, and chemical energy in food or fuel. When you kick a football, chemical energy from your muscles transfers to kinetic energy in the ball.

Renewable energy sources like wind, solar, and hydro-electricity won't run out, but they can be unreliable and expensive to set up initially. Wind turbines only work when it's windy, and solar panels need sunlight. However, they produce no pollution once they're running.

Non-renewable sources like coal, oil, and gas provide about 80% of our energy because they're reliable and cost-effective. The problem? They're slowly running out and add to greenhouse gases that cause global warming. Nuclear energy is incredibly powerful but can be dangerous to handle and dispose of.

Quick tip: Remember that energy can never be created or destroyed - it just transfers from one store to another. This is the conservation of energy.

The specific heat capacity tells you how much energy you need to heat 1kg of a substance by 1°C. Materials with high specific heat capacity (like water) take loads of energy to heat up, which is why the sea stays cool in summer.

Electricity and Circuits

Your home runs on 230V mains electricity at 50Hz frequency, delivered through the national grid at voltages up to 400,000V. The live wire (brown) carries the current, neutral (blue) completes the circuit, and earth $yellow/green$ keeps you safe.

Static electricity happens when electrons build up on objects through friction - like when you rub a balloon on your hair. Remember: like charges repel, opposite charges attract. Only electrons move, never protons.

Circuit components behave differently depending on conditions. LDRs (light dependent resistors) have high resistance in darkness and low resistance in bright light. Thermistors are temperature-dependent - as they heat up, their resistance drops.

In series circuits, current flows through each component one after another - if one breaks, they all stop working. Parallel circuits split the current between branches, so if one component fails, the others keep working.

Remember: In series circuits, current is the same everywhere but voltage is shared. In parallel circuits, voltage is the same across each branch but current is shared.

Ohmic conductors have constant resistance when temperature stays the same. Filament bulbs aren't ohmic because their resistance increases as they heat up.

Atomic Structure and Radiation

Density equals mass divided by volume $ρ = m/V$, measured in kg/m³. Solids are usually densest because particles are packed tightly together, whilst gases have very low density because particles are spread far apart.

The particle model explains that all matter is made of constantly moving particles. In gases, particles move faster and collide more as temperature increases, creating pressure. Internal energy is the total kinetic and potential energy of all particles in a substance.

Atomic models have evolved from Dalton's solid spheres to our current understanding. The nucleus contains protons and neutrons, with electrons orbiting in energy levels. Isotopes have the same number of protons but different numbers of neutrons.

Radioactive decay is completely random and gives off three types of radiation. Alpha particles (helium nuclei) are stopped by paper and highly ionising. Beta particles $high-speed electrons$ penetrate aluminium and are moderately ionising. Gamma rays are electromagnetic waves that penetrate concrete and are weakly ionising.

Key fact: Half-life is the time taken for half the radioactive nuclei in a sample to decay - this helps us predict how long radioactive materials remain dangerous.

Background radiation comes from space, rocks, and human activities. We measure radiation using Geiger-Muller tubes. Nuclear fission splits large nuclei to release energy (used in power stations), whilst fusion combines small nuclei (happens in stars).