17.8 - Potential Dividers

A potential divider shares a voltage between two resistors

• A potential divider is a circuit that splits a supply voltage between two resistors in series.
• It allows a circuit to take a smaller voltage from a larger supply.
• The supply's potential difference is shared between the two resistors in the ratio of their resistances: the larger a resistor's share of the total resistance, the larger its share of the voltage.

Because the same current passes through both resistors in series, a larger resistance has a larger potential difference across it.

Worked through with numbers

A 9 V supply is connected across a 2 Ω resistor and a 1 Ω resistor in series, as shown in the circuit below.

• Total resistance = 2 + 1 = 3 Ω.
• The 2 Ω resistor takes 2/3 of the supply: 2/3 of 9 V = 6 V.
• The 1 Ω resistor takes 1/3 of the supply: 1/3 of 9 V = 3 V.
• The two shares add up to the 9 V supply.