AQA GCSE Physics Higher Tier Paper 1 Summary Notes

Methods of Storing Energy from Wind Turbines:
- Method A: Heating water to a high temperature. Energy stored per $100\,kg$ is $33\,600\,kJ$ with $40\%$ energy wasted. Can be installed anywhere.
- Method B: Pumping water uphill to a reservoir. Energy stored per $100\,kg$ is $490\,kJ$ with $25\%$ energy wasted. Requires high mountains.
Energy Stores: Heating water increases its thermal energy store, while pumping water uphill increases its gravitational potential energy store.
Environment and Climate Change: Reducing carbon dioxide ( $CO_2$ ) emissions from transport and electricity generation slows climate change. Examples include switching to electric vehicles for transport and using renewable sources instead of fossil fuels for electricity.

Nuclear Fission Process: In nuclear power stations, energy is released from uranium nuclei. The uranium nucleus splits into two parts and releases three neutrons. This process also releases electromagnetic radiation in the form of gamma rays.
Energy Output Calculation: Power output $P$ is linked to energy $E$ and time $t$ by the equation $E = P \times t$ .
- With a power output of $500\,MW$ ( $500 \times 10^{6}\,W$ ) and a time of $3600\,s$ , the energy output is calculated as $1.8 \times 10^{12}\,J$ .
Radioactive Waste: Waste with a long half-life is a significant hazard. Precautions include deep underground burial or heavy shielding to prevent radiation exposure.
Operational Efficiency: For a power station generating electricity for $92\%$ of a year ( $365$ days), the operational time is $335.8$ days.

Resistance and Length: In a wire at constant temperature, resistance is directly proportional to length. A low potential difference (e.g., $1.50\,V$ ) is not an electrical hazard because it is too low to cause a significant current through a human body.
Mains Electricity (UK): The standard frequency is $50\,Hz$ and the potential difference is $230\,V$ .
Power and Resistance: Resistance $R$ can be calculated from power $P$ and current $I$ using $P = I^2 \times R$ . For a coin dissipating $340\,mW$ at $0.75\,A$ , the resistance is approximately $0.604\,\Omega$ .
Thermistors: Thermistor resistance decreases as temperature increases. Dirty coins may fail recognition in vending machines due to increased contact resistance.
Plug and Fuses: The live wire in a three-core cable is brown. A fuse wire melts when current becomes too great.
- Current calculation ( $I = \frac{Q}{t}$ ): For a charge flow of $2.0\,C$ in $400\,ms$ , current is $5.0\,A$ .
- Specific latent heat calculation ( $E = m \times L$ ): To find the mass $m$ using energy $1.02\,J$ and latent heat $60\,kJ/kg$ .

Metal Domes and Static Charge: A dome can be negatively charged by a motor-driven rubber belt. A student’s hair stands up when touching the dome because each hair gains the same negative charge and they repel each other.
Electric Fields: A region where a charged object experiences a non-contact force. Field strength decreases as distance from the charged object increases.
Sparks: A spark transfers energy when the potential difference between two points is high enough to ionize the air. Increasing the potential difference increases the distance a spark can jump.

Gas Pressure: In a fixed mass of air at constant temperature, decreasing the volume increases pressure because gas particles collide with the walls more frequently.
Work Done and Temperature: Compressing air quickly (e.g., in a fire piston) involves work being done on the gas, which increases the mean kinetic energy of the particles and results in a temperature rise.
Energy Calculations: Specific heat capacity of air is given as $1.01\,kJ/kg\,^{\circ}C$ . The temperature change $\Delta\theta$ is determined by $\Delta E = m \times c \times \Delta\theta$ .
Elastic Potential Energy: In a bungee ride, stretching the cords increases the elastic potential energy store. The maximum height reached is influenced by energy losses to the surroundings (e.g., air resistance).

Detecting Radiation: Count rates are measured using a radiation detector (e.g., Geiger-Müller tube). Alpha radiation has a short range in air (a few centimeters); if the count rate drops to background levels within $5\,cm$ , the source is an alpha emitter.
Absorption: Beta radiation is stopped by aluminum, while gamma radiation is reduced by thick lead. These materials distinguish between radiation types.
Safety: To reduce dose, use long-handled tongs (distance) or lead containers (shielding). To avoid contamination, wear gloves or protective clothing.
Activity: Activity is the rate of decay of unstable nuclei, measured in Becquerels ( $Bq$ ).