Physics paper 1

• 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
• Energy must be transferred from one object to another or one store to another store in a closed system
• 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

  1. Divide both sides by mass to get velocity

  2. Square root both sides to get velocity
• 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
• Work is another word for energy used
• Specific heat capacity practical

  1. Use an electric heater, voltmeter, ammeter to measure power

  2. Measure mass and temperature change of a material

  3. Use the equation energy = mass * specific heat capacity * temperature change to find the specific heat capacity
• Power


  Rate of energy transfer, calculated as energy / time
• Efficiency


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


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

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


  Rate of flow of electric charge, calculated as charge / time
• Resistance


  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 changes (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


  Unit is 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
• The change in gradient of the I-V curve for a metal shows that its resistance increases with higher PD and current
• Metals


  Consist of a lattice of ions surrounded by a sea of delocalized electrons, which collide with the ions more frequently at higher currents, increasing resistance
• Resistors are specially made so their resistance stays constant even if 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)


  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 linear relationship between resistance and wire length
• Series circuit


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