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
• If more energy is transferred 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 set time
• 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, measured in volts
• Current


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


  The property of a component that resists the flow of electric current, measured in ohms
• Increasing potential difference


  Increases current in a resistor (Ohm's law)
• Resistance of a resistor is constant (ohmic), but resistance of a bulb changes (non-ohmic)
• 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
• Steeper gradient of the line

  Lower the resistance of the resistor
• Ohm's law


  V = I * R (PD in volts = current in amps * resistance in ohms)
• Resistance of a component

  Can be found from an IV graph by rearranging Ohm's law to R = V/I
• Graph for a bulb

  • Curved graph
  • Resistance is changing
  • Resistance of the metal filament increases with higher PD and current
• Metals consist of a lattice or grid of ions surrounded by a sea of delocalized electrons
• Higher current leads to more frequent collisions between electrons and ions, making the ions vibrate more and increasing resistance
• Resistors are specially made from specific materials so their resistance stays constant even if temperature changes
• Diode


  • Only lets current flow through in one direction
  • In one direction the resistance is very high, in the other it is very low
• LED (light emitting diode)


  Similar to a diode but emits light as well
• 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 the sum of all resistances
• Potential divider circuit


  Series circuit where total PD is shared between components
• 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


  • Rate of energy transfer
  • P = VI or P = I^2R