Potential Dividers | Physics for GCSE/IGCSE - Year 11 PDF Download

Variable Potential Dividers

• When two resistors are linked in series, they divide the potential difference across the power source between them.

A potential divider splits the potential difference of a power source between two components

• The potential difference across individual resistors varies according to their resistance.
  • The resistor with the greatest resistance will encounter a greater potential difference than the other resistor.
  • Increasing the resistance of one resistor results in it receiving a larger fraction of the potential difference, while the remaining resistor receives a reduced fraction.
• A potentiometer is a component consisting of a coil of wire with a sliding contact at its midpoint.
  
• When the slider is moved upwards, the resistance in the lower portion increases, causing a rise in the potential difference across it.
  
• Moving the slider upward in the diagram raises the resistance of the lower section, causing an increase in the potential difference across it.

Resistors as Potential Dividers

• When two resistors are connected in series, according to Kirchhoff's Second Law, the potential across the power source gets distributed between them. 
• Potential dividers, essentially circuits, create an output voltage that is a fraction of the input voltage. 
• These dividers serve two primary functions: 
  • one, to offer a variable potential difference, and 
  • two, to allow for a specific potential difference selection, 
  • thus dividing the power source's potential among multiple components.
• The concept of potential dividers is extensively utilized in various applications including volume controls and sensory circuits that incorporate Light Dependent Resistors (LDRs) and thermistors.
• In a potential divider circuit, the output voltage ratio is determined by the resistor values. This ratio equals the ratio of resistances of the resistors within the circuit. The relationship can be mathematically expressed as follows:
  
• Where:
  • R₂ is the numerator and the resistance of the resistor over Vout
  • R₁ is the other resistance in series
  • V_out is the output potential difference
  • V_in is the input potential difference
• The potential divider equation can also be expressed as:
  
• When considering electrical resistance, 
• R₁ represents the numerator and signifies the resistance of the resistor over Vout. 
• Meanwhile, R₂ denotes the other resistance present in series. 
• Irrespective of the notation utilized, the outcome will always be the same. 
  • It is essential for the numerator to signify the resistance of the resistor over V_out.

Understanding Potential Divider Circuits

• The input voltage (V_in) is connected across two series resistors.
• The output voltage (V_out) is measured across one of the resistors (R₂).
• The voltage across each resistor is determined by its resistance (R):
  • The resistor with higher resistance will have a greater voltage drop.
  • According to Ohm's Law (V = IR), if the resistance of one resistor increases, it takes a larger proportion of the total voltage, leaving less for the other resistor.
• In a potential divider circuit, the voltage across a resistor is directly proportional to its resistance (V = IR).