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Potentiometer
Intermediate
Compares emfs without drawing current.
A uniform wire with steady current compares emfs by balancing potential drops along the wire without drawing current from the cell, so it measures true EMF.
ε₁/ε₂ = l₁/l₂.
More accurate than a voltmeter.
In more detail
A potentiometer compares voltages by balancing them against a uniform potential gradient along a wire. It measures EMF without drawing current from the cell.
Real-world uses
- Measuring EMFs of cells accurately.
- Volume controls and dimmers use potentiometers as variable resistors.
- Physicists use a potentiometer to measure the emf of a cell accurately, without drawing any current from the cell.
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Frequently asked questions
Why not use a voltmeter?
A voltmeter draws some current, which lowers the reading, while a potentiometer does not at balance.
What is a potential gradient?
The uniform fall of voltage along a current-carrying wire.
Why does drawing no current matter?
A voltmeter that draws current measures a reduced voltage, while a potentiometer gives the true emf.
Related topics in Current Electricity & Circuits
Kirchhoff's voltage law · Wheatstone bridge · Meter bridge · Ammeter and voltmeter · Galvanometer · Multimeter