paper 1

• Energy is not something you can hold in your hand, it's just an idea
• Total energy in any interaction is always conserved, energy cannot be created or destroyed
• Energy can be turned into matter (Mass) but it's still technically true that energy cannot be created or destroyed
• Energy stores


  Different types of energy
• Kinetic energy


  Calculated using e = 1/2 mv^2
• Gravitational potential energy (GPE)


  Calculated using e = mgh
• Elastic potential energy


  Calculated using e = 1/2 ke^2
• Thermal energy


  Calculated using e = mc∆T
• Chemical potential energy is found in food and fuels, but there is no equation for it
• In a closed system, no energy is lost to the surroundings and no energy comes in from the surroundings
• Gravitational potential energy at the top of a roller coaster

  Converted to kinetic energy at the bottom
• If more energy is lost to the surroundings than expected, the system is not closed
• Specific heat capacity practical

  Use an electric heater, voltmeter, ammeter, balance, timer, and thermometer to measure the specific heat capacity of a material
• Power


  The rate of energy transfer, calculated using P = E/t
• Efficiency


  The ratio of useful energy output to total energy input, calculated as useful energy out / total energy in
• Insulation practical for triple physics: wrap cans in different insulating materials and measure temperature after a certain time
• Electricity


  The flow of electric charge (electrons) that carries energy from a source to a component
• Potential difference (PD) / Voltage

  The amount of energy transferred per unit of charge, calculated using V = E/Q
• Current


  The rate of flow of electric charge, calculated using I = Q/t
• Resistance


  The property of a component that resists the flow of electric current, described by Ohm's law V = IR
• Resistance of a resistor is constant (ohmic), but resistance of a bulb changes (non-ohmic)
• PD and current or V and I

  Directly proportional
• Drawing a graph of PD and current makes a straight line
• Turning the battery round gives negative values for PD and current but still a straight line through the origin
• Straight line with constant gradient

  Shows that a resistor has constant resistance
• Steeper gradient of the line

  Lower the resistance of the resistor
• Ohm's law


  V = I * R
• For a resistor, the resistance calculated from an IV graph is the same regardless of the point on the line
• For a bulb, the resistance calculated from an IV graph depends on the point chosen as the resistance is changing
• Reason for changing resistance in a metal

  Collisions between free electrons and vibrating ions increases as current and PD increase
• Resistors are specially made so their resistance stays constant even if temperature changes
• Diode


  Only allows current to flow in one direction
• LED


  Light emitting diode, acts like a diode but also emits light
• Measuring resistance of a metal wire

  1. Connect wire to circuit with crocodile clips

  2. Measure V and I

  3. Calculate R using Ohm's law

  4. Move one clip to change wire length

  5. Observe how resistance changes with length
• Series circuits


  • Total PD is shared between components
  • Current is the same for all components
  • Total resistance is the sum of all resistances
• Parallel circuits


  • PD is the same for each branch
  • Current is shared between branches
  • Total resistance decreases as more resistors are added
• Thermistor


  Resistance decreases as temperature increases
• LDR


  Light dependent resistor, resistance decreases as light intensity increases
• Power


  Rate of energy transfer, can be calculated as P = VI or P = I^2R
• DC (direct current)


  Current that only flows in one direction