Paper 1 - AQA Physics

• System


  An object or group of objects
• When a system changes

  The way energy is stored also changes
• Ball rolling and hitting a wall

  • Moving ball
  • Kinetic energy transfers as sound
• Vehicle slowing down

  • Vehicle moving
  • Kinetic transfers to thermal due to friction
• Kinetic Energy

  𝐸𝐸𝑘𝑘 = 1

  2 𝑚𝑚𝑣𝑣2
• Elastic Potential Energy

  𝐸𝐸𝑒𝑒 = 1

  2 𝑘𝑘𝑒𝑒2
• Gravitational Potential Energy

  𝐸𝐸𝑝𝑝 = 𝑚𝑚𝑚𝑚ℎ
• Specific Heat Capacity

  • The energy required to raise the temperature of 1kg of a substance by 1°C or 1K
  • 𝐸𝐸 = 𝑚𝑚𝑚𝑚∆𝑇𝑇
• Power

  𝑃𝑃 = 𝐸𝐸

  𝑡𝑡 = 𝑊𝑊

  𝑡𝑡
• An energy transfer of 1 joule per second is equal to a power of 1 watt
• If given two motors A and B, the motor that can do the same work faster

  Is more powerful
• Energy can be transferred usefully, stored or dissipated but cannot be created or destroyed
• In all system changes energy is dissipated, so that it is stored in less useful ways. This energy is often described as being 'wasted'
• Reducing energy waste


  • Lubrication
  • Thermal Insulation
• Thermal Conductivity


  The higher the thermal conductivity of a material, heat is allowed to travel through the material more easily, so the higher the rate of energy transfer by conduction across the material
• If the walls are thin metal sheets


  Heat would be lost very quickly
• Efficiency


  • The ratio of the useful work done by a machine, engine, device, etc, to the energy supplied to it, often expressed as a percentage
  • 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒��𝑒𝑒𝑒𝑒𝑒𝑒𝑒 = 𝑢𝑢𝑢𝑢𝑒𝑒𝑢𝑢𝑢𝑢𝑢𝑢 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑚𝑚𝑒𝑒 𝑜𝑜𝑢𝑢𝑡𝑡𝑝𝑝𝑢𝑢𝑡𝑡

  𝑡𝑡𝑜𝑜𝑡𝑡𝑡𝑡𝑢𝑢 𝑒��𝑒𝑒𝑒𝑒��𝑒𝑚𝑚𝑒𝑒 𝑒𝑒𝑒𝑒𝑝𝑝𝑢𝑢𝑡𝑡
• Ways to increase efficiency

  • Reducing waste output
  • Recycling waste output
• Main Energy Sources


  • Non-renewable: Fossil Fuels, Nuclear Fuel
  • Renewable: Biofuel, Wind, Hydro-electricity, Geothermal, Tidal, Solar, Water waves
• Renewable energy


  Energy which can be replenished as it is used
• Non-renewable energy


  Used more for large-scale energy supplies due to the large energy output per kilogram of fuel
• Renewable energy has become more important due to the finite lifetime of fossil fuels, and so their development has become more important
• Renewable energy is not always the most reliable as: solar doesn't work in bad weather or night, wind is only intermittent
• Main Energy Uses


  • Transport
  • Electricity generation
  • Heating
• Environmental Impact of Energy

  • Extraction: Fossil fuels destroy landscapes, wind turbines can be an eyesore
  • Use: Fossil fuels release harmful emissions, solar/wind create electricity with no emissions
• During industrial revolution, fossil fuels became an important source of energy as it was easy to mine, and provided a lot of energy
• Only recently has renewable energy become more suitable – technology has had to develop a lot since industrial revolution to be able to harness such energy sources efficiently
• It is easier to use energy resources due to increasing pressure to cope with the public's increasing power demands but harder to solve environmental issues due to political, social, ethical and economic considerations
• Electrical Charge


  • Circuit must be closed (no open switches)
  • There must be a source of potential difference (battery/cell)
• Electrical Current


  • Flow of electrical charge
  • Greater the rate of flow of charge, greater current
  • Q = It (Charge = Current x Time)
• In a single closed loop, the current has the same value at any point
• Current, potential difference and resistance

  V = IR (Potential Difference = Current x Resistance)
• Resistors


  • If resistance is constant, current is directly proportional to potential difference (linear graph)
  • If resistance changes with current, graph is non-linear (e.g. lamps, diodes, thermistors, LDRs)

  
• How resistance changes


  1. With current (as current increases, electrons have more energy and collide more with atoms, increasing resistance)

  2. With temperature (normal wires - atoms vibrate more when hot, thermistors - resistance decreases in hotter temperatures)

  3. With length (greater length means more resistance)

  4. With light (LDRs - greater light intensity, lower resistance)

  5. With voltage (diodes - allow current in one direction only)
• Series Circuits


  Closed circuit, current follows single path, total resistance is sum of individual resistances

  
• Parallel Circuits


  Branched circuit, current splits into multiple paths, total resistance is less than smallest individual resistance
• In a series circuit, potential difference is shared across the whole circuit and current is the same through all parts
• In a parallel circuit, potential difference is the same across all branches and current is shared between the branches
• Mains electricity in the UK is AC (alternating current) with a frequency of 50 Hz and voltage of 230 V
• Mains Electricity Cabling


  • Live wire (brown, 230 V)
  • Neutral wire (blue, 0 V)
  • Earth wire (green/yellow, 0 V, safety wire)