A rheostat is a variable resistor used to control the current flowing in a circuit. It consists of a resistive wire wound around a cylindrical core, with a sliding contact (also known as a wiper) that can be moved along the wire to vary the resistance. The covered rheostat is designed to protect the user from accidental electrical contact with the resistive wire.

The wire is typically housed inside a protective casing made of insulating materials such as ceramic or plastic. The sliding contact is connected to two terminals, and by adjusting the position of the contact along the wire, the resistance can be varied, allowing for control of the current flowing through the circuit. Covered rheostats are commonly used in scientific and engineering applications, such as in electrical power transmission and in electronic circuit design.