Phys Paper 1

• 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 system
  • Kinetic energy transfers to sound
• Vehicle slowing down


  • Moving vehicle system
  • Kinetic energy transfers to thermal due to friction
• Kinetic Energy


  𝐸𝐸𝑘�� = 1

  2 𝑚𝑚��𝑣2
• Elastic Potential Energy


  𝐸𝐸𝑒�� = 1

  2 𝑘𝑘��𝑒2
• 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 = 𝑚𝑚��𝑚∆𝑇𝑇
• Power


  • The rate at which energy is transferred or the rate at which work is done
  • 𝑃𝑃 = 𝐸𝐸

  𝑡𝑡 = 𝑊𝑊

  𝑡𝑡
• 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
• 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
• Thermal conductivity in a building

  Rate of cooling is low if walls are thick and thermal conductivity of the walls are low
• 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
  • efficiency = useful energy output

  total energy input

  = useful power output

  total power input
• 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
• Renewable energy is not always the most reliable
• Main Energy Uses


  • Transport
  • Electricity generation
  • Heating
• Environmental Impact


  • Extraction of Energy: Fossil fuels destroy landscapes, Wind turbines can be considered an eyesore
  • Use of Energy Sources: Fossil fuels release harmful emissions, Solar and wind directly 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


  For charge to flow: Circuit must be closed (no open switches), There must be a source of potential difference (battery/cell)
• Electrical Current


  Current is the flow of electrical charge, Greater the rate of flow of charge, greater current, Q = It where Q is the charge flow, I is the current, and t is the time
• In a single closed loop, the current has the same value at any point
• Current, potential difference and resistance


  The current (I) through a component depends on both the resistance (R) of the component and the potential difference (V) across the component, V = IR
• Ohmic conductors


  • If the resistance is constant, current is directly proportional to the potential difference, graph is linear
• Non-ohmic conductors


  • If the resistance of components such as lamps, diodes, thermistors and LDRs is not constant, it changes with the current through the component, so the graph is nonlinear
• How resistance changes with current

  As current increases, electrons (charge) has more energy, When electrons flow through a resistor, they collide with the atoms in the resistor, This transfers energy to the atoms, causing them to vibrate more, This makes it more difficult for electrons to flow through the resistor, So resistance increases, and current decreases
• How resistance changes with temperature

  Normal wires - Same process as current, atoms vibrate more when hot, Thermistor - In hotter temperatures the resistance is lower
• How resistance changes with length

  The greater the length, the more resistance and the lower the current, Electrons have to make their way through more resistor atoms, so it is harder than using a shorter wire
• How resistance changes with light

  LDR (Light Dependent Resistor) - The greater the intensity of light, the lower the resistance, So the resistance is greatest when it is dark
• How resistance changes with voltage

  Diodes - Diode allows current to flow freely in one direction, In the opposite direction, it has a very high resistance so no current can flow