Resistance in series and parallel

• Total resistance of resistors in series

  Resistors in series add together
• Calculating current in a circuit with resistors in series

  1. Calculate total resistance

  2. Divide potential difference by total resistance
• Resistors in series


  • Current has to pass through each resistor in turn, cannot bypass any resistor
• Equivalent resistance


  Resistors in series can be replaced by one resistor with the combined resistance
• Circuit with resistors in series

  • 20 ohm
  • 15 ohm
  • 10 ohm
• Calculating potential difference across resistors in series

  1. Calculate total resistance

  2. Multiply resistance by current
• Total resistance of resistors in parallel


  Less than the resistance of the smallest individual resistor
• Resistors in parallel


  • Two pathways for current, more total current flows
• You are not expected to calculate the total value from resistors in parallel