Physics Paper 1

• Energy isn't 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/types of energy

  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Thermal energy
  • Chemical potential energy
• Calculating kinetic energy

  e = 1/2 mv^2 (energy = 1/2 mass x velocity^2)
• Calculating gravitational potential energy

  e = mgh (energy = mass x gravitational field strength x height)
• Calculating elastic potential energy

  E = 1/2 ke^2 (energy = 1/2 spring constant x extension^2)
• Calculating thermal energy/change in thermal energy

  e = mcΔT (energy = mass x specific heat capacity x temperature change)
• An increase in thermal energy results in particles moving faster
• We don't really talk about sound or vibrational energy as this is just kinetic energy of particles
• Chemical potential energy is found in food and fuels
• Energy transfers in a closed system

  Energy cannot be lost or gained, it is just transferred between stores
• Gravitational potential energy at the top of a roller coaster

  Kinetic energy at the bottom
• If energy is lost to the surroundings, 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, measured in Watts (Joules per second)
• Calculating power

  P = E/t (Power = Energy / time)
• Efficiency

  A measure of how much of the input energy is usefully used, calculated as useful energy out / total energy in
• Insulation practical (triple only)
• Energy sources

  Where energy is harnessed from, e.g. fossil fuels, nuclear, renewable sources
• Electricity

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

  The energy transferred per unit of charge, measured in Volts
• Calculating potential difference

  V = E/Q (Potential difference = Energy / Charge)
• Current

  The rate of flow of electric charge, measured in Amperes
• Calculating current

  I = Q/t (Current = Charge / time)
• Resistance

  The opposition to the flow of electric current, measured in Ohms
• Ohm's law

  V = IR (Potential difference = Current x Resistance)
• Resistance of a resistor is constant (Ohmic), resistance of a bulb varies (non-Ohmic)
• Current (I) and Voltage (V)

  Directly proportional
• Drawing a graph of current (I) and voltage (V) makes a straight line
• Reversing the battery gives negative values for both current and voltage, but the straight line through the origin remains
• Constant gradient of the straight line

  Shows that a resistor has constant resistance, which is called 'ohmic'
• Steeper gradient of the straight line

  The lower the resistance of the resistor, as more current is flowing per volt
• Ohm's law

  V = I * R, where V is potential difference in volts, I is current in amps, and R is resistance in ohms
• For a resistor, the resistance calculated from the I-V graph is the same regardless of the point chosen on the line
• For a bulb, the I-V graph is curved, showing that the resistance is changing
• Reason for changing resistance in metals

  Metals consist of a lattice or grid of ions surrounded by a sea of delocalized electrons, which collide with the ions more frequently as current and temperature increase, making it harder for the electrons to flow and increasing the resistance
• Resistors are specially made from materials such that their resistance stays constant even if the 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 similar to a diode, but also emits light