What is a Rheostat?

Here you will find out what rheostats are if you are among those who are interested. In this article, we want to talk about what is rheostats, how they work, their types and function, and so on. 

What is a Rheostat?

The Wikipedia definition of a rheostat is a two-terminal variable resistor. The resistor has been designed to control current flow throughout a circuit. Additionally, a rheostat can change the resistance of the circuit without disrupting it. It is commonly believed that these adjustable resistors are the same as potentiometers. The main difference between them is that they only use two terminals.

The rheostat symbol is easy to understand as well. Rheostat symbols vary according to standards, but the most commonly used is a rectangle placed between two linear lines; a tilted arrow crosses the rectangle.

Types of rheostats

Let’s now explore the world of different rheostat types. Different types of rheostats are available on the market, but three of them are more popular than the rest. Rotary, linear, and preset are the three most popular types. The most common type is the rotary rheostat.

1.     Rotatory rheostat.

This type, as mentioned above, is the commonly used one. Rotating rheostats are most commonly used in power applications. Rotation is the determining factor of its resistance. The shaft mounted to the wiper of the rheostat will change the length that affecting the resistance as it moves.

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2.     Linear rheostat

There are some similarities in the working principle of linear and rotary rheostats. However, the rotary rheostat’s movement determines resistance in each. Instead of rotary rheostats, linear rheostats have a linear movement for changing the length. Laboratory rheostats usually adhere to this type of movement. Linear rheostats change resistance by sliding their sliding terminals along a linear path. The slider will have only one terminal connected to a rheostat if it is being used.

3.     Preset rheostat

Third, the most popular type of rheostat is the preset rheostat. Printed circuit boards (also known as PCBs) are typically made of this type. If rheostats are used in PCBs, they are preset rheostats; if used elsewhere, they are trimmers. Inside such circuits, preset rheostats are used for calibration.

There are two terminals (and even three) on this small rheostat, but only one fixed terminal is connected. It’s important to remember that even a three-terminal rheostat only has two terminals. In addition to using potentiometers as rheostats, potentiometers can be configured for many other purposes.

Construction of rheostat

Rheostat construction is almost identical to that of a potentiometer. Potentiometers and rheostats both have three terminals: terminal A, terminal B, and terminal C. However, we only use two terminals: A and B or B and C. The two fixed terminals are A and C, which are connected to both ends of the resistive element. In contrast, terminal B is the variable terminal connected to the sliding wiper.

The rheostat changes its resistance with the wiper moving across the resistive element. The resistance of a rheostat is changed by moving the slider or wiper along the resistance path. A coil of wire or a thin film of carbon makes up the resistive element.  

The resistive element is usually made up of a coil of wire. Rheostats are, therefore, sometimes referred to as variable wire wound resistors. Rheostats are generally made by winding Nichrome wire around an insulating ceramic core. Rheostats have ceramic cores that act as heat insulators. Consequently, the ceramic core does not allow heat through it.

How does a rheostat regulate the flow of current in a circuit?

To change the current in a circuit, either the voltage or the resistance must change. A rheostat can change the circuit’s current by changing the circuit’s resistance. A circuit whose resistance is increased will have less current. Therefore, if you need to increase the current, you need to decrease the resistance.

Three factors affect resistance and, therefore, the current: length, type, and cross-section area. Length is the most significant factor for a rheostat. Changing length is accomplished by moving the contact in a rheostat, which changes resistance, which, in turn, changes the current.

Can a rheostat reduce voltage?

Changing the current is the primary function of a rheostat. The voltage across the rheostat would always be the same when placed across a voltage source. If the resistance is increased, the current will decrease. Since the voltage source is fixed, the two other factors should also change to affect the voltage. In basic electrical engineering, this is known as V=IR (V stands for voltage, I for current, and R for resistance).

Because rheostats change the current, and the voltage stays the same, they should change the resistance to influence the current, affecting the voltage. Since the two items that affect voltage change via rheostat is also possible to control voltage with a rheostat.

What is the purpose of a rheostat?

Although rheostats are used for various purposes, their primary use is controlling the current in a circuit. In addition to being voltage dividers, they can also be used as variable resistive loads. Thermistors are also used in testing laboratories and electrical workshops for testing purposes.

Using a rheostat, you can test different circuits with various currents. As a bonus, the circuits in those labs can be tested under different voltage conditions. Lighting circuits are another common application for rheostats. They can be used as dimming devices in such circuits.

What’s the difference between a potentiometer and a rheostat?

Both the potentiometer and the rheostat are made the same way. There is only one difference: how we used them. With potentiometers, all three terminals are used to operate, whereas only two terminals are used with rheostats.

Applications of the rheostat

A rheostat is commonly used for applications that require high voltage or current.

  • In dim lighting, rheostats are used to control light intensity. We can decrease the flow of electric current through the light bulb by increasing the resistance of the rheostat. Consequently, the brightness of the light will decrease. 
  • We can also increase the flow of electricity through a light bulb by decreasing its resistance. Consequently, the brightness of the light will increase.
  • A rheostat is used to adjust the radio’s volume and the speed of an electric motor.

FAQs (Frequently Asked Questions)

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