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 due to an object's 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 due to the random motion of particles, calculated as mass * specific heat capacity * temperature change
• 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) 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

  1. Perform the opposite operation on both sides to cancel out the other variables
  2. Simplify the equation
• Work is just another word for energy used
• Specific heat capacity practical

  Use an electric heater to heat a metal block

  1. Measure the power of the heater using a voltmeter and ammeter
  2. Measure the mass of the block and the temperature increase
  3. Use the formula: energy = power * time to calculate the energy transferred
  4. Use the formula: energy = mass * specific heat capacity * temperature change to calculate 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, calculated as useful energy out / total energy in
• Electricity


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

  The energy transferred per unit of charge, calculated as energy / charge
• Current


  The rate of flow of electric charge, calculated as charge / time
• Resistance


  The opposition to the flow of electric current, described by Ohm's law: V = IR
• Resistors have constant resistance, shown by a straight line on an I-V graph
• Bulbs have variable resistance, shown by a curved line on an I-V graph
• 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 it harder for electrons to flow, increasing resistance
• Resistors are specially made so their resistance stays constant even if temperature changes
• Diode


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


  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 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