Physics Paper 1

• Energy is not a thing that you can hold, it's something that objects and particles have
• Energy is always conserved, it can't be destroyed or created, just transferred
• Different stores of energy

  • Kinetic
  • Gravitational or gravitational potential
  • Electric potential
  • Nuclear
  • Thermal
  • Elastic potential
  • Vibrational
  • Chemical potential
  • Sound
• Work done


  A posh name for the energy transferred by a force
• Gravitational potential energy (GPE) at the top

  Equal to the kinetic energy (KE) at the bottom (in an ideal situation with no energy loss)
• If there is resistance or friction


  Some of the GPE is turned into KE, and some is lost
• Hooke's law


  Force a spring is pulled with = stiffness x extension
• Describing Hooke's law practical

  • Line up zero mark on ruler with bottom of spring
  • Have ruler close to spring with eye in line to reduce parallax error
  • Use 100g and 1000g slotted masses
  • Measure extension
  • Plot force on y-axis, extension on x-axis
  • Gradient gives spring constant
• Power


  Rate of energy transfer, joules per second
• Efficiency


  How much of the input energy/power is used usefully
• Impossible to get 100% efficiency in any energy transfer
• Renewable energy sources


  • Wind (kinetic energy)
  • Solar (electromagnetic waves)
  • Tidal (kinetic energy)
  • Hydroelectric (kinetic energy)
• Non-renewable energy sources


  • Coal, oil, gas (chemical potential energy)
  • Nuclear (nuclear energy)
• Insulators


  Reduce heat transfer via conduction
• Insulation practical


  • Use identical cans/beakers
  • Fill with same volume of water at same initial temp
  • Vary number of insulation layers
  • Measure temp decrease over 10 mins
  • Control room temp, use lids to reduce convection
• Atoms are neutral, with equal numbers of protons and electrons
• Atomic symbol


  Bottom number = number of protons (= number of electrons)

  Top number = mass number (protons + neutrons)
• Isotopes


  Same element, different mass number (different number of neutrons)
• Alpha radiation


  Helium nucleus, highly ionizing but low penetrating power
• Beta radiation


  Fast moving electron, medium ionizing and penetrating power
• Gamma radiation


  High energy electromagnetic waves, weakly ionizing but highly penetrating
• Radioactivity


  Number of decays per second in a radioactive sample
• Half-life


  Time taken for radioactivity to decrease to half its original value
• After 3 half-lives, radioactivity is 1/8 of original value
• Nuclear fission


  Heavy nucleus splits into two or more lighter nuclei, releasing energy and neutrons
• Nuclear fusion


  Light nuclei combine to form a heavier nucleus, releasing energy
• Ohm's law


  V = IR
• Voltage (V) or Potential Difference (PD)

  Energy per unit charge lost/gained as charge passes through a component
• Current (I)


  Rate of flow of electric charge
• Resistance (R)


  How hard it is for current to flow through a component
• IV characteristic graph for a resistor is a straight diagonal line
• Coulomb


  A group of electrons
• We don't deal with individual electrons because otherwise our numbers would be absolutely tiny but we group them together into coulombs to make it easier
• Voltage or PD


  Energy divided by charge (joules per Coulomb)
• Current (I)


  The rate of flow of charge (coulombs per second)
• Resistance (R)


  How hard it is for current to flow through a component (unit is Ohm)
• The IV (current-voltage) characteristic graph for a resistor is a straight diagonal line that goes positive and negative
• The gradient of the IV graph does not give the resistance, you need to use Ohm's law (V=IR) to find the resistance
• LDR (light dependent resistor) and thermistor


  • They are ohmic so long as the conditions stay the same
  • LDR has low resistance in high light, high resistance in low light
  • Thermistor has low resistance when hot, high resistance when cold
• Diode


  A component that only lets current flow in one direction