Electronics - Voltage and Current - Discussion

Both answers are correct. It is 3 terminal but only 2 terminals are used. Explained as below.

Rheostat is a variable resistor, which is used to control the flow of electric current by manually increasing or decreasing the resistance. The electric current flowing through an electrical circuit is determined by two factors: the amount of voltage applied and the total resistance of the electrical circuit. If we reduce the circuit resistance, the flow of electric current through the circuit will be increased. On the other hand, if we increase the circuit resistance, the flow of electric current through the circuit will be decreased.

By placing the rheostat in the electrical circuit, we can control (increase or decrease) the flow of electric current in the circuit. Rheostat reduces the electric current flow to certain level. However, it does not completely blocks the electric current flow. To completely block the electric current flow, we need infinite resistance. Practically it is not possible to completely block the electric current.

Like the potentiometer, the rheostat also consists of three terminals: terminal A, terminal B and terminal C. However, we use only two terminals: either A and B or B and C. Terminal A and terminal C are the two fixed terminals connected to both ends of the resistive element called track and terminal B is the variable terminal connected to the sliding wiper or slider. The wiper that moves along the resistive element varies the resistance of the rheostat. The resistance of the rheostat is changed when the slider or wiper is moved over the resistive path. The resistive element of the rheostat is made of a coil of wire or a thin carbon film.

Rheostats are mostly wire wound. Hence, rheostats are also sometimes referred as variable wire wound resistors. Generally, rheostats are made by winding the Nichrome wire around an insulating ceramic core. The ceramic core of the rheostat acts as the insulating material to the heat. Hence, the ceramic core does not allow heat through it.

Rheostat is a three terminal device that controls current, but answer is two terminal, could anyone please clarify this.

The answer is the rheostat is a 2 terminal device. But @FAISAL said it is 3 terminal. Which one is correct ?

Rheostat is an adjustable or variable resistor. It is used to control the electrical resistance of a circuit without interrupting the flow of current. Rheostat has 3 terminals and usually consist of a resistive wire wrapped to form a toroid coil with a wiper that slides along the surface of the coil. It is most often designed with a ceramic core. Rheostats are used in applications that require high voltage and current.

A potentiometer is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider[1]. If only two terminals are used (one side and the wiper), it acts as a variable resistor or rheostat. Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment