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


  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, 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
• Rearranging equations to find unknown variables

  1. Divide both sides by mass to get v = sqrt(2gH)

  2. Divide both sides by charge to get V = E/Q
• If more energy is transferred to the surroundings than the measured temperature change, the calculated specific heat capacity will be higher than the true value
• Power


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


  Ratio of useful energy output to total energy input, calculated as useful energy out / total energy in
• Electricity


  The flow of electric charge, which transfers energy from a source to a component
• Potential difference (voltage)


  The 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 current, described by Ohm's law V = IR
• Resistance of a resistor is constant, but resistance of a bulb changes with current
• PD and current or V and I

  Directly proportional
• Graph of PD and current

  • Straight line
  • Negative values for both but still a straight line through the origin
  • Constant gradient shows a resistor has constant resistance
• Resistance


  Ohm's law: V = I * R
• Resistance of a resistor

  Steeper the gradient of the line, the lower the resistance
• Resistance of a bulb


  Resistance is changing, shown by a curved graph
• Metals consist of a lattice or grid of ions surrounded by a sea of delocalized electrons
• As current increases


  Resistance of metal increases
• Resistors are specially made from specific material such that their resistance stays constant even if the temperature changes
• Diode


  Only lets current flow through in one direction
• LED


  Light emitting diode, acts similar to a diode but 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 see how length affects resistance
• Series circuit


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


  • PD is the same for every branch
  • Current is shared between each branch
  • 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 that only flows in one direction
• Alternating current (AC)


  Current that alternates direction, from mains electricity
• In a plug, the fuse is attached to the live wire and designed to melt/blow if current exceeds a certain value
• Calculating fuse size for an appliance

  1. Use P = VI to find current

  2. Choose next fuse size up from calculated current