Physics Paper 1 - Key Concepts
Nuclear reactions are some of the most powerful processes in the universe. Nuclear fission happens when large, unstable nuclei split apart, releasing massive amounts of energy - this is how nuclear power plants and atomic weapons work. The process creates a chain reaction as neutrons from one split nucleus cause others to split too.
Nuclear fusion works the opposite way, joining two light nuclei (like hydrogen) to form a heavier one (like helium). This process powers the sun but requires incredibly high temperatures and pressures to work. Some mass gets converted directly into energy, which is why both fusion and fission release so much power.
Radioactivity comes in three main types: alpha particles (2 protons + 2 neutrons, don't travel far but cause lots of damage), beta particles (electrons, travel moderately far), and gamma rays (electromagnetic waves that penetrate very far but cause less damage). Half-life tells you how long it takes for half the radioactive nuclei in a sample to decay.
Quick Tip: Remember that alpha particles are the most dangerous if they get inside your body, but gamma rays are hardest to block from the outside.
Energy cannot be created or destroyed - it just transfers between different stores like kinetic, gravitational potential, thermal, and chemical. Specific heat capacity (ΔE = mcΔθ) tells you how much energy you need to heat up 1kg of a substance by 1°C. Power measures how quickly energy transfers happen.
Gas particles move constantly in random directions. When they move faster or collide more frequently, pressure increases. Pressure and volume are inversely proportional - squeeze a gas into half the space and you'll double the pressure.
Static electricity forms when electrons jump between materials during rubbing. This leaves one material positively charged and the other negatively charged. Like charges repel, opposite charges attract.
Electrical circuits work through current (flow of charge), potential difference (the driving force), and resistance (what slows the flow down). In series circuits, everything shares the current but voltage splits up. In parallel circuits, voltage stays the same but current splits between branches.
