What is a rheostat, I explain its principle of operation, device and designation in a simple and accessible way

If you and I take some simple device and carefully study its circuitry, then it is likely that we can find a rheostat there. In this material, I will simply and clearly explain what a rheostat is in essence, on what principle it works, and also how widely it is used in the world. So, let's begin.

What is a rheostat

So, for starters, let's define a rheostat. A rheostat is a variable resistor, the electrical resistance of it between its moving contact and the terminals of the resistive element can be changed mechanically.

At its core, a rheostat is nothing more than a control element in electrical circuits. And perhaps the main advantage of this element is that it is quite possible to use it to adjust the electrical resistance in the circuit without breaking it.

How a rheostat works

If we take any physics textbook for the eighth grade, we will find out that the operation of a rheostat is based on the famous Ohm's law for a circuit section. So, the electric current passing through the circuit undergoes a change depending on the level of resistance, it (the current) collides with it at a constant source voltage.

So, if there is low resistance in the circuit under consideration, then a high electric current will flow through it, since practically nothing interferes with it. And accordingly, if there is a high resistance in the circuit, then a small electric current will flow through it.

This very ratio was used (and is still used) for fine-tuning the circuit parameters depending on specific requirements.

If we carefully look at the above photo, we will see that a structurally simple rheostat represents It is a hollow cylinder with an insulated wire wound around it, which has a constant cross section and resistance along its entire length.

This was done for a reason. After all, the resistance of any conductor in the first place has a linear dependence on its length and is inversely proportional to the cross-sectional area. So in the same physics textbook you can find the following formula:

Where p is the resistivity of the conductor material;

I is the length of the considered conductor;

S is the cross-sectional area of ​​the conductor.

So, if the conductor in question has a constant cross section, then the greater its length, the greater its resistance.

That is, in fact, a rheostat is a large piece of wire wound on a base, and the resistance value is changed by the slider, which increases or, conversely, reduces the length of the conductor (changes resistance).

Note. Any rheostat is designed for a certain maximum resistance, as well as for the permissible current strength, the excess of which will inevitably lead to overheating and failure of the element. In this case, all parameters are indicated on the product itself.

How is the rheostat indicated on the diagrams

In the diagrams, the rheostat has the following designation:

From the designation it immediately becomes clear that when the slider is moved to the right side, the resistance will decrease, and to the left it will increase.

In foreign literature, the designation of the rheostat is different and looks like this:

And this element is always included in the circuit in a sequential manner. This is because electric current always follows the path of least resistance. Therefore, if you and I include a rheostat in the circuit in a parallel way, then it will not work in this version. The correct inclusion in the rheostat circuit is as follows:

Well, now let's look at where rheostats are mainly used.

Scope of rheostats

In fact, the scope of rheostats is quite wide. So if we take, for example, a water heater, then nothing more than a rheostat is used to regulate the heating of the heating element.

If you take an old radio, then the volume control there is also carried out by rheostats. Also, in lamps with dimming bulbs, a regulator is often used, which is based on a simple rheostat.

In modern electronics, rheostats are replaced by electronic controllers (semiconductor elements, potentiometers, etc.), since they have practically no losses.

The thing is that rheostats have one significant disadvantage. When the current strength in the circuit changes, the rheostat heats up quite a lot, as a result of which a lot of energy is spent on heating.

That's all I wanted to tell you about such an element as a rheostat.

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