Rheostat vs. Potentiometer: Key Differences Explained

This article explores the distinctions between rheostats and potentiometers, two devices used to vary resistance in circuits, thereby controlling current or voltage.

Rheostat

• A rheostat is a two-terminal device.
• It’s connected in series with the load and voltage source.
• The primary function of a rheostat is to vary the current in a circuit.
• As the wiper (adjustable contact) moves, the resistance changes. Moving the wiper “up” (in a typical schematic representation) increases resistance, while moving it in the opposite direction decreases it.
• Crucially, a rheostat must have a wattage rating sufficient to handle the maximum current ($I$) when the resistance ($R$) is at its minimum value.

Potentiometer

• A potentiometer is a three-terminal device.
• Its end terminals are connected across a voltage source.
• The third, variable arm (wiper) taps a portion of the applied voltage.
• The applied voltage ($V$) serves as the input to the two end terminals.
• The output voltage ($V_{out}$), which is variable, is measured between the wiper and one of the end terminals.
• A potentiometer can function as a rheostat. This is achieved by using only the wiper terminal and one of the other terminals, leaving the third terminal unconnected and unused.