Potential dividers are electric circuits that divide the potential difference across two or more components (often two resistors) in order to produce a specific output. Potential dividers function by the fact that the p.d. across each resistor depends on its resistance:
This can also be expressed as “the potential divider equation”:2
Potential dividers can also be used with variable components to produce a varying output voltage based on conditions.
- Thermistor: R2 is replaced with a thermistor. If temperature rises, the number electron density rises so the thermistor’s resistance falls. This means that Vout
- LDR: replace R1 with an LDR. If the light intensity increases, the number electron density rises so the LDR’s resistance falls. Hence, the p.d. across the LDR falls and the p.d. across R2 rises, increasing V.
- Potentiometer: works in the same way but R1 and R2 are combined into a variable resistor with three terminals and a sliding contact. Adjusting the contact varies the p.d. between two of the terminals, giving a variable Vout.