5.2.9 Potential Divider Circuits

• When two resistors are connected in series, through Kirchhoff’s Second Law, the potential difference across the power source is divided between them
• Potential dividers are circuits that can produce an output voltage as a fraction of its input voltage
• The main purposes of a potential divider are:
  • To provide a variable potential difference
  • To enable a specific potential difference to be chosen
  • To split the potential difference of a power source between two or more components

• Potential dividers have a wide range of applications in devices requiring features such as volume control and sensory circuits
  • This can be achieved using components such as LDRs and thermistors

• Potential divider circuits are based on the ratio of voltage between components
• This is equal to the ratio of the resistances of the resistors in the diagram below, giving the following equation:

Potential divider diagram and equation

• The input voltage V_in is applied to the top and bottom of the series resistors
• The output voltage V_out is measured from the centre to the bottom of resistor R₂
• The potential difference V across each resistor depends upon its resistance R:
  • The resistor with the largest resistance will have a greater potential difference than the other one from V = IR
  • If the resistance of one of the resistors is increased, it will get a greater share of the potential difference, whilst the other resistor will get a smaller share

• In potential divider circuits, the p.d across a component is proportional to its resistance from V = IR