Physics (UK GCSE)
UK GCSE Physics deck aligned with AQA, Edexcel, OCR and WJEC specifications. Covers energy, electricity, particle model, atomic structure, forces, waves, magnetism, electromagnetism, and space physics for Years 10-11 (ages 14-16).
Ämne: Fysik · Nivå: Högstadium (13–15) · 453 kort
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- Energy is measured in joules (J). One joule equals the work done when a force of one newton moves an object one metre in the direction of the force.
- The eight energy stores are: kinetic, gravitational potential, elastic potential, thermal, chemical, nuclear, magnetic and electrostatic.
- Energy can be transferred mechanically (by a force), electrically (by a current), by heating, or by radiation (light and sound).
- Kinetic energy is calculated by KE = ½ m v², where m is mass in kg and v is speed in m/s.
- Gravitational potential energy is calculated by GPE = m g h, where m is mass in kg, g is gravitational field strength (9.8 N/kg on Earth) and h is height in metres.
- Elastic potential energy is calculated by EPE = ½ k e², where k is spring constant (N/m) and e is the extension or compression in metres.
- Work done is calculated by W = F s, where F is force in newtons and s is distance moved in the direction of the force in metres. One joule of work is done per newton per metre.
- Power is the rate of energy transfer: P = E/t. It is measured in watts (W), where one watt equals one joule per second.
- The principle of conservation of energy states that energy can be transferred, stored or dissipated but cannot be created or destroyed.
- Efficiency is the ratio of useful energy output to total energy input: efficiency = useful output / total input. It can also be calculated using power: efficiency = useful power output / total power input.
- Wasted energy is usually dissipated as thermal energy to the surroundings. This raises the temperature of the surroundings but the energy becomes too spread out to be useful.
- Specific heat capacity (c) is the energy required to raise the temperature of 1 kg of a substance by 1 °C. Energy transferred: E = m c Δθ, measured in J/kg°C.
- Thermal conductivity is a measure of how well a material conducts thermal energy. Metals are good thermal conductors; gases and insulating materials such as wool are poor conductors.
- Ways to reduce unwanted energy transfers in a home include loft insulation, cavity wall insulation, double glazing, draught excluders and thick walls. They reduce conduction, convection and radiation.
- Renewable energy resources include solar, wind, hydroelectric, tidal, wave, geothermal and biofuel. They will not run out within a human timeframe.
- Non-renewable energy resources include coal, oil, natural gas and nuclear fuel (uranium). Fossil fuels release carbon dioxide when burned, contributing to climate change.
- The National Grid is the system of cables and transformers that carries electricity from power stations to consumers across the UK. It uses step-up and step-down transformers.
- Step-up transformers increase the voltage to very high values (e.g. 400 000 V) for long-distance transmission. This reduces current, so less energy is lost as heat in the cables.
- Step-down transformers reduce voltage to safe levels (e.g. 230 V) for homes and offices before electricity reaches consumers.
- Solar cells generate electricity directly from sunlight. They have no fuel cost and no greenhouse emissions in use, but are weather and time-of-day dependent.
- Electric current is the rate of flow of charge: I = Q/t. Current is measured in amperes (A) using an ammeter connected in series.
- Potential difference (voltage) is the energy transferred per unit charge: V = E/Q. It is measured in volts (V) using a voltmeter connected in parallel across a component.
- Resistance is the opposition to current flow: R = V/I. It is measured in ohms (Ω).
- Ohm's law states that the current through a fixed resistor is directly proportional to the potential difference across it, provided temperature stays constant: V = IR.
- In a series circuit, the same current flows through every component; the total potential difference of the supply equals the sum of voltages across the components; and total resistance is the sum of the individual resistances.
- In a parallel circuit, the potential difference is the same across each branch; the total current is the sum of the currents in each branch; and adding more branches decreases total resistance.
- An I-V graph for a fixed resistor is a straight line through the origin — current is proportional to voltage (ohmic behaviour).
- An I-V graph for a filament lamp is an S-shaped curve. As current increases, the filament heats up, resistance rises, so the gradient (1/R) decreases.
- A diode only allows current to flow in one direction. Its I-V graph shows almost zero current when reverse-biased and rapidly rising current after a small forward voltage.
- A thermistor has high resistance at low temperatures and lower resistance at higher temperatures. It is used in temperature sensors and thermostats.
- A light-dependent resistor (LDR) has high resistance in the dark and lower resistance in bright light. It is used in light sensors and automatic street-light circuits.
- UK mains electricity is alternating current (a.c.) at 230 V and a frequency of 50 Hz. The waveform changes direction 100 times per second.
- A direct current (d.c.) supply such as a battery makes charge flow in one direction only. Cells and batteries supply d.c.
- A three-pin UK plug has three wires: live (brown) at 230 V, neutral (blue) at about 0 V, and earth (green and yellow stripes) at 0 V used for safety.
- The earth wire carries no current in normal use. If a fault makes the casing live, the earth wire provides a low-resistance path so a large current blows the fuse and breaks the circuit.
- A fuse contains a thin wire that melts when the current exceeds its rating. This breaks the circuit and protects the appliance and user. Common fuse ratings are 3 A, 5 A and 13 A.
- Electrical power can be calculated by P = IV or P = I²R. Energy transferred by an appliance: E = Pt = IVt, measured in joules.
- Electric charge is measured in coulombs (C). Q = I t, so one coulomb is the charge that passes when a current of one ampere flows for one second.
- Static electricity is produced when insulating materials are rubbed together. Electrons transfer, leaving one material negatively charged and the other positively charged.
- Like charges repel, unlike charges attract. A charged object can attract small uncharged objects by induction (electrons in the uncharged object move).
- An electric field surrounds any charged object. The field lines around a positive point charge point outward; around a negative charge they point inward.
- Circuit symbols: a battery is shown as long and short parallel lines, a resistor as a rectangle, a switch as a gap with a hinged line, and a lamp as a circle with a cross inside.
- Density is mass per unit volume: ρ = m/V. It is measured in kg/m³ (SI) or g/cm³ in everyday use.
- In a solid, particles are tightly packed in a regular pattern and vibrate about fixed positions. Solids have fixed shape and volume.
- In a liquid, particles are close together but can slide past each other. Liquids have fixed volume but take the shape of their container.
- In a gas, particles are far apart and move randomly at high speed. Gases have neither fixed shape nor fixed volume and are easily compressed.
- Internal energy is the sum of kinetic energy and potential energy of all the particles in a system. Heating a system increases its internal energy.
- Specific latent heat is the energy needed to change the state of 1 kg of a substance without changing its temperature: E = m L, measured in J/kg.
- Specific latent heat of fusion is the energy required to melt 1 kg of solid (or freeze 1 kg of liquid). Specific latent heat of vaporisation is the energy to boil 1 kg of liquid (or condense 1 kg of gas).
- On a heating curve, flat sections represent state changes. Temperature stays constant while energy goes into breaking bonds rather than increasing kinetic energy of particles.