AQA - physics 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 e = 1/2 mv^2
• Gravitational potential energy (GPE)


  Energy an object has due to its position in a gravitational field, calculated as e = mgh
• Elastic potential energy


  Energy stored in a stretched or compressed spring, calculated as e = 1/2 kx^2
• Thermal energy


  Energy transferred due to a temperature difference, calculated as e = mcΔT
• Chemical potential energy


  Energy stored in chemical bonds, e.g. in food or fuels
• In a closed system, no energy is lost to the surroundings and no energy comes in from the surroundings
• Gravitational potential energy (GPE)


  Converted to kinetic energy (KE) as an object falls
• Work is just another word for energy used
• 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 as P = E/t
• Efficiency


  The ratio of useful energy output to total energy input, calculated as efficiency = useful energy out / total energy in
• Electricity


  The flow of electric charge, which carries energy from a source to a component where it is released as another form of energy
• Potential difference (PD) / Voltage

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


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


  The property of a component that opposes the flow of electric current, described by Ohm's law V = IR
• Resistance of a resistor is constant (ohmic), but resistance of a bulb varies (non-ohmic)
• 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 (PD in volts = current in amps * resistance in ohms)
• Resistance of a component can be found from an I-V graph by rearranging Ohm's law to R = V/I
• For a resistor, the resistance value is the same regardless of the point on the I-V line used
• For a bulb, the I-V graph is curved, showing that resistance is changing
• Resistance of metal


  Increases with higher PD and current, due to increased collisions between electrons and ions
• Resistors are specially made so their resistance stays constant with temperature changes
• Diode


  Only allows current to flow in one direction, with very low resistance in one direction and very high resistance in the other
• LED (light emitting diode)


  Similar to 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 straight line relationship between resistance and wire 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


  P = VI or P = I^2R
• Direct current (DC)


  Current only flows in one direction