Topic 10 ~ Electricity and Circuits

• Subatomic Particle


  • Proton
  • Neutron
  • Electron
• Proton


  Relative Mass: 1, Relative Charge: +1
• Neutron


  Relative Mass: 1, Relative Charge: 0
• Electron


  Relative Mass: 0 (0.0005), Relative Charge: -1
• Series Circuits


  • Closed circuit
  • The current is the same everywhere
• Parallel Circuits


  • Branched circuit
  • Current splits into multiple paths
  • Total current into a junction = total current in each of the branches
  • Voltage is the same across each "branch"
• Potential Difference


  • Measured in Volts
  • Energy transferred per unit charge, Joule per Coulomb
  • Measured across two points, as it is the amount of energy per unit charge to move from one point to the next
  • Measured with a voltmeter, placed in parallel across a component
  • There can be a voltage across a component, in a closed or open circuit
  • When it is in a closed circuit, and there is a potential difference (voltage), current will always flow
• Current


  • Measured in amps
  • Rate of flow of charge (the flow of electrons in the wires)
  • Measured at any single point on the circuit
  • Measured with ammeter which is placed in series
• Resistance


  • Greater resistance, the harder it is for charge to flow through the component, therefore the current is smaller
  • Variable resistor changes the amount of resistance of the component, changing the amount of current that flows in the circuit
• Series Circuits


  • Components are connected end to end
  • All the current flows through all the components
  • Can only switch them all off at once
  • PD (potential difference) is shared across the whole circuit
  • PD of power supply = sum of PD across each component
  • Current is the same through all parts of the circuit
  • Current at one point = current at any other point
  • Total Resistance is the sum of the resistance in each component R1 + R2 = R
• Parallel Circuits


  • Components are connected separately to the power supply
  • Current flows through each one separately
  • You can switch each component off individually
  • PD is the same across all branches
  • PD of power supply = PD of each branch
  • Current is shared between each of the branches
  • Current through source = sum of current through each branch
  • Total resistance is less than the branch with the smallest resistance
• Resistance changes with


  • Current
  • Temperature
  • Length
  • Cross Sectional Area
  • Light
  • Voltage
• As current increases, electrons (charge) has more energy
• When electrons flow through a resistor, they collide with the ions in the resistor
• The current here is doing work against the resistance
• This transfers energy to the ions, causing them to vibrate more (heating resistor)
• This makes it more difficult for electrons to flow through the resistor, so resistance increases, and current decreases
• Thermistor


  Hotter temperatures, resistance is lower
• LDR (Light Dependent Resistor)


  Greater the intensity of light, the lower the resistance
• Diode


  Allows current to flow freely in one direction, in the opposite direction it has a very high resistance, so no current can flow
• Efficiency – low resistance wires means less energy loss as current flows through the circuit
• Testing Relationships


  1. Make sure component(s) do not overheat, leave to cooldown between each reading

  2. Repeats and take average

  3. Varied wire resistance

  4. Filament Lamps

  5. Diodes

  6. LDR

  7. Thermistor
• AC (Alternating Current)


  Current continuously varies, from positive to negative (charge changes direction)
• DC (Direct Current)


  Movement of charge in one direction only
• In the UK, mains supply is at 50Hz and 230V
• Plug


  • Live wire (brown, carries voltage from mains to appliance)
  • Neutral Wire (blue, completes the circuit)
  • Earth wire (green and yellow stripes, safety wire used to stop the appliance becoming live)
• Fuse


  Connected to the live wire, if a large current passes through live wire, fuse heats up and melts, breaking the circuit – preventing a fire or damage
• Power Rating


  The power of the appliance when in use, greater power rating means greater energy consumption per second