Reostaadi

Reostaadi, known in English as a rheostat, is a two-terminal variable resistor used to control current or power in an electric circuit by changing resistance. It is designed to handle higher currents than typical small-signal resistors and is thus suited for power adjustment tasks.

Most reostaadi are either wire-wound or carbon-based. The common form consists of a resistive element with a sliding or rotating contact (the wiper) that taps into different portions of the element, thereby varying the total resistance. They can be linear or circular and are rated by power, from a few watts up to hundreds of watts. The construction emphasizes robustness and heat dissipation, as higher currents can produce significant heat.

Operation: When connected in series with a load, increasing the resistance reduces current according to Ohm's law (I = V/R). Because power dissipation P = I^2R, rheostats can become hot, requiring adequate heat sinking or ventilation. They are typically used where a simple, rugged method of adjusting current is needed.

Applications: Historically used to adjust lamp brightness, motor speed, or heater power in laboratory setups and industrial equipment. With the rise of electronic controllers, their role has diminished, but rugged, high-current adjustment remains advantageous in some environments.

Difference from potentiometer: Unlike a three-terminal potentiometer used as a voltage divider, a rheostat uses two terminals and is intended as a variable resistor rather than a divider.

Origin and notes: The device emerged in the 19th century during early electrical experimentation and equipment. Today, reostaadi is more often replaced by solid-state or electronic controllers, though traditional rheostats remain in use for certain high-power or rugged applications.