A voltmeter and a potentiometer can both be used to determine voltage, but they work differently in classical electrical measurement. A voltmeter measures potential difference directly by connecting across two points and drawing a small current. A DC potentiometer uses a null-balance method, comparing an unknown EMF with a known voltage so that, at balance, ideally no current is drawn from the source being measured.
The term “potentiometer” also commonly means a three-terminal variable resistor, so context matters.
At a glance
| Point | Potentiometer (measurement instrument) | Voltmeter |
|---|---|---|
| Method | Null/balance comparison | Direct measurement |
| Current from source at ideal balance | Zero/negligible | Small but nonzero because input resistance is finite |
| Loading error | Very low at null | Depends on input resistance relative to source/circuit |
| Use | Precision EMF measurement/calibration in classical labs | Routine voltage measurements |
| Reading speed | Requires balancing in traditional form | Immediate digital/analog reading |
| Modern electronics meaning | ‘Potentiometer’ often means variable resistor/voltage divider | Still a measuring instrument |
Potentiometer (measurement instrument)
A null-method device that compares an unknown EMF/potential difference with a calibrated reference along a resistive element.
Voltmeter
An instrument connected in parallel to measure potential difference directly.
Why input resistance matters
A voltmeter becomes part of the circuit when connected. If its input resistance is not much larger than the circuit impedance, the measured voltage can change—a loading effect.
Modern digital multimeters often have very high input resistance, making loading small in many ordinary circuits.
Null measurement advantage
At balance, a classical potentiometer does not draw current from the cell whose EMF is being measured. That lets it estimate open-circuit EMF more accurately than a low-resistance direct meter.
Do not confuse the two meanings of potentiometer
In electronics shopping, a potentiometer is usually the rotary/slider component used for volume controls and adjustable voltage dividers. In older physics-lab questions, ‘potentiometer’ often refers to the precision comparison apparatus.
Frequently asked questions
Can a voltmeter measure EMF?
It can approximate open-circuit voltage, but finite loading can matter; a null potentiometer is the classical high-accuracy method.
How is a voltmeter connected?
In parallel across the two points being measured.
What happens if a voltmeter has low resistance?
It can significantly alter the circuit and produce measurement error.
Is a potentiometer always a measuring device?
No. In modern electronics the word usually means an adjustable resistor/voltage divider.
KnowDifferences Editorial Team
Independent explanations with definitions, practical examples and references. Read our editorial approach.