Potentiometer | CIE AS Physics Revision Notes 2025

The potentiometer

A potentiometer is similar to a variable resistor connected as a potential divider to give a continuously variable output voltage
It can be used as a means of comparing potential differences in different parts of the circuit
The circuit symbol is recognised by an arrow next to the resistor

Potentiometer circuit symbol

Potentiometer symbol, downloadable AS & A Level Physics revision notes

A potentiometer circuit symbol looks like a resistor with an arrow towards it

A potentiometer is a single component that (in its simplest form) consists of a coil of wire with a sliding contact, midway along it

A potentiometer

Potentiometer diagram, downloadable AS & A Level Physics revision notes

A potentiometer is a type of variable resistor

It is recognised on a circuit diagram with a resistor fitted with a sliding contact
The sliding contact has the effect of separating the potentiometer into two parts (an upper part and a lower part), both of which have different resistances

Potentiometer circuit diagram

Potentiometer circuit diagram, downloadable AS & A Level Physics revision notes

Moving the slider (the arrow in the diagram) changes the resistance (and hence potential difference) of the upper and lower parts of the potentiometer

If the slider in the above diagram is moved upwards, the resistance of the lower part will increase and so the potential difference across it will also increase
Therefore, the variable resistor obtains a maximum or minimum value for the output voltage
If the resistance is 3 Ω:
- Maximum voltage is when the resistance is 3 Ω
- Minimum voltage is when the resistance is 0 Ω

Worked example

A potential divider circuit consists of fixed resistors of resistance 5.0 Ω and 7.0 Ω connected in series with a 6.0 Ω resistor fitted with a sliding contact. These are connected across a battery of e.m.f 12 V and zero internal resistance, as shown.What are the maximum and minimum output voltages of the circuit with the sliding contact?

	Maximum voltage / V	Minimum voltage / V
A.	8.7	4.7
B.	6	0
C.	12	6.5
D.	12.5	4.7

Answer: A

Step 1: List the known quantities:

Input voltage, V_in = 12 V
First resistor, R₁ = 5.0 Ω
Second resistor, R₂ = 6.0 Ω
Third resistor, R₃ = 7.0 Ω

Step 2: Determine the maximum and minimum resistance with the sliding contact

When the sliding contact is at the top of the 6.0 Ω resistor, the output voltage takes into account the 6.0 Ω and 7.0 Ω resistor
When the sliding contact is at the bottom of the 6.0 Ω resistor, the output voltage only takes into account the 7.0 Ω

Step 3: State the potential divider equation for the three resistors

This time, R₂ and R₃ are on the numerator as they are where V_outis from

$V_{o u t} = (\frac{R_{2} + R_{3}}{R_{1} + R_{2} + R_{3}}) V_{i n}$

Step 3: Calculate the maximum output voltage

This is when the sliding contact is at the top of the 6.0 Ω resistor

$V_{o u t} = (\frac{6.0 + 7.0}{5.0 + 6.0 + 7.0}) \times 12.0 = 8.7 V$

Step 4: Calculate the minimum output voltage

This is when the sliding contact only covers the 7.0 Ω resistor

$V_{o u t} = (\frac{7.0}{5.0 + 6.0 + 7.0}) \times 12.0 = 4.7 V$

Potentiometer (CIE AS Physics)

Revision Note

The potentiometer

Potentiometer circuit symbol

A potentiometer

Potentiometer circuit diagram

Worked example

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Author: Ashika