P4: electrical circuits

• Potential difference


  A measure of how much energy is transferred between two points in a circuit, what pushes electrical charge around the circuit
• Current


  The flow of electrons through an electrical conductor, the amount of charge passing at a certain point per second
• Resistance


  The opposition to the flow of charge, something stopping it
• Current = Charge / Time
• Current has the symbol I, Charge has the symbol Q, Time has the symbol T
• Resistance is measured in Ohms
• 15 circuit symbols to know for GCSE

  • Cell
  • Bulb
  • Ammeter
  • Voltmeter
  • Diode
  • Light Emitting Diode
  • Resistor
  • Variable Resistor
  • Light Dependent Resistor
  • Fuse
  • Thermistor
  • Buzzer
  • Motor
  • Switch (closed)
  • Switch (open)
• Calculating resistance across a length of wire

  1. Vary length of wire

  2. Keep temperature constant

  3. Keep thickness of wire constant

  4. Use Ohm's law (Resistance = Voltage / Current)
• Series circuits


  • Current can only flow in one path, if there is a fault the whole circuit breaks
• In a series circuit, the current is the same everywhere
• In a series circuit, the voltage splits up across components
• In a series circuit, the total resistance is the sum of all the resistances
• Parallel circuits


  • Current has multiple paths it can go down, if one component breaks the others will still work
• In a parallel circuit, the current splits up across the branches
• In a parallel circuit, the voltage is the same everywhere
• As voltage increases for a resistor

  Current increases proportionally
• As voltage increases for a light bulb

  Resistance increases, creating an S-shaped graph
• As voltage increases for a diode


  Current only flows in one direction, creating a diode-shaped graph