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


  Energy of motion, calculated as 1/2 * mass * velocity^2
• Gravitational potential energy (GPE)

  Energy an object has due to its position in a gravitational field, calculated as mass * gravitational field strength * height
• Elastic potential energy


  Energy stored in a stretched or compressed spring, calculated as 1/2 * spring constant * extension^2
• Thermal energy


  Energy associated with the random movement of particles, calculated as mass * specific heat capacity * temperature change
• Chemical potential energy


  Energy stored in chemical bonds, e.g. in food or fuels
• For anything to happen in a system, energy must be transferred from one object to another or one store to another store
• In a closed system, no energy is lost to the surroundings and no energy comes in from the surroundings
• Gravitational potential energy (GPE) at the top of a roller coaster


  Converted to kinetic energy (KE) at the bottom
• Rearranging equations to find unknown variables

  Isolate the variable you want to find

  2. Perform the opposite operation on both sides to move the variable to the left side

  3. Simplify the equation
• If the total energy at the top of a roller coaster is greater than the total energy at the bottom, the difference must have been lost to the surroundings
• The specific heat capacity practical involves heating a material and measuring the temperature change to determine the specific heat capacity
• Power


  The rate of energy transfer, calculated as energy / time
• Efficiency


  The ratio of useful energy output to total energy input, expressed as a decimal or percentage
• Electricity


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

  The amount of energy transferred per unit of charge, measured in volts
• Current


  The rate of flow of electric charge, measured in amperes
• Resistance


  The property of a component that opposes the flow of electric current, measured in ohms
• Ohm's law states that potential difference (V) is directly proportional to current (I) for a resistor, with the constant of proportionality being the resistance (R)
• The resistance of a resistor is constant, but the resistance of a light bulb changes as the current through it changes
• PD and current or V and I

  Directly proportional
• Drawing a graph of PD and current makes a straight line
• Reversing the battery 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
• Resistor


  Ohmic - the steeper the gradient, the lower the resistance
• Ohm's law


  V = I * R
• Resistance


  Unit is ohms
• Resistance of a component can be found from an I-V graph by rearranging Ohm's law
• For a resistor, the resistance value is the same regardless of the point on the line
• For a bulb, the resistance is changing so the resistance value depends on the point on the curved line
• Reason for changing resistance in metals

  Collisions between free electrons and vibrating ions increases as current and temperature increase
• Resistors are specially made so their resistance stays constant with 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
• Resistance and length of wire are directly proportional
• Series circuit


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