Summary
Highlights
Energy is an abstract concept, conserved in all interactions (cannot be created or destroyed, except in mass-energy conversions for triple science). Different 'stores' of energy exist, measured in Joules. These include kinetic energy (E=1/2mv^2), gravitational potential energy (E=mgh), elastic potential energy (E=1/2ke^2), and thermal energy (E=mcΔT). Chemical potential energy is also mentioned as being in food or fuels.
Energy is transferred between objects or stores within a system. In a closed system, total energy is conserved. Examples such as a roller coaster converting GPE to KE demonstrate this. Work done against forces like air resistance causes energy loss to surroundings. The specific heat capacity practical is discussed, outlining how to measure it and common sources of error. Power is defined as the rate of energy transfer (P=E/t), and efficiency as the ratio of useful energy out to total energy in.
Insulation in houses reduces heat loss. A practical for testing insulation is described. Energy sources are explained, differentiating between finite (non-renewable) sources like fossil fuels and nuclear fuel, and renewable sources like wind, hydroelectric, solar, geothermal, and biofuel.
Electricity is the flow of charge (electrons), carrying energy from a source to a component. Circuits must be complete loops. Potential difference (PD), or voltage, is the energy transferred per Coulomb of charge (V=E/Q). Current is the rate of flow of charge (I=Q/t). Voltmeters measure PD in parallel, and ammeters measure current in series.
Components have resistance, which impedes charge flow. Ohm's Law (V=IR) relates PD, current, and resistance. Resistors have constant resistance (ohmic), while bulbs and other metals have variable resistance (non-ohmic) due to increased atomic vibrations at higher temperatures. Diodes permit current flow only in one direction.
A practical to investigate the relationship between wire length and resistance is explained. Series and parallel circuits are compared: in series, PD is shared, current is constant, and total resistance adds up; in parallel, PD is constant, current is shared, and adding more resistors decreases total resistance.
Thermistors and Light Dependent Resistors (LDRs) change resistance with temperature and light intensity, respectively, enabling their use in sensors. Electrical power can also be calculated as P=VI or P=I^2R.
DC (Direct Current) flows in one direction (e.g., from batteries), while AC (Alternating Current) periodically reverses direction (e.g., mains electricity). Mains wiring includes neutral, live, and earth wires, with the earth wire providing a safety pathway for current. Fuses are safety devices that melt if current exceeds a safe limit. Calculating the appropriate fuse for an appliance is demonstrated.
The National Grid uses transformers to step up voltage for efficient transmission (reducing current and heat loss) and then step it down for safe domestic use. Static electricity (triple science) involves charge transfer when insulating materials rub, leading to attraction or repulsion of charged objects and the creation of electric fields.
Density (ρ=m/V) measures how compactly mass is packed and depends on particle type and arrangement. Measuring density for regular and irregular objects (using a displacement can) is covered. The three states of matter (solid, liquid, gas) are described based on particle arrangement and movement. Transitions between states require energy to overcome inter-particle forces.
Internal energy is the sum of kinetic and potential energy of particles. During temperature changes, kinetic energy changes (E=mcΔT). During phase changes, temperature remains constant while potential energy changes (E=mL), this is called latent heat.
Heating a gas increases particle kinetic energy, leading to more frequent and forceful collisions with container walls, thus increasing pressure. Compressing a gas also increases pressure by doing work on it. For a gas at constant temperature, pressure and volume are inversely proportional (P₁V₁ = P₂V₂).
Alpha radiation (helium nucleus) is highly ionizing but easily absorbed. Beta radiation (fast electron) is less ionizing but more penetrating, stopped by aluminum. Gamma radiation (high-energy EM wave) is weakly ionizing but highly penetrating, reduced by lead or concrete. Measuring radiation with a GM tube and correcting for background radiation is discussed. Uses of each type of radiation (smoke detectors, thickness gauges, medical treatments) are mentioned.
Radioactivity is the rate of decay, measured in Becquerels (Bq). This rate decreases over time. Half-life is the time it takes for radioactivity (or the number of unstable nuclei/mass) to halve. How to determine half-life from a graph and solve related calculations are explained.
Nuclear fission (e.g., uranium-235) is when a heavy nucleus splits, releasing energy, smaller nuclei, and more neutrons, leading to a chain reaction. This is harnessed in nuclear reactors to generate electricity. Nuclear fusion (e.g., hydrogen in the Sun) is when light nuclei combine to form a heavier one, also releasing energy. Fusion is challenging to replicate on Earth due to the extreme conditions required.
The evolution of atomic models (Thomson, Rutherford, Bohr, Chadwick) is reviewed. Atoms are characterized by atomic number (protons) and mass number (protons + neutrons). Isotopes are atoms of the same element with different neutron numbers. Radiation includes electromagnetic waves (gamma rays, emitted from the nucleus) and particles (alpha and beta).