When looking at any circuit, whether electrical or electronic, we will find a number of electrical resistors distributed in more than one place, and this indicates their great importance and the role they play to complete the circuit and carry out the required work. Regardless of their different types, they can often be distinguished by a cylindrical shape with colored lines indicating the The value of the resistance, which makes using it very easy. However, if you want to know how electrical resistors work, you must address the topic from all its aspects and in a little more depth.

Definition of electrical resistance

It is one of the basic parts used in electrical circuits to limit the electrical current passing through it. Various materials are used in their manufacture, such as carbon, metal oxides, metal films, and current-resistant wire, and they are made in various sizes, including large ones made of wire, some with terminals, all the way to small types used in electronic circuits. As a result of the different types of electrical resistors, each type is characterized by its own properties and characteristics, and therefore each type is used in a specific field.

In order for the electrical circuit to work as expected, the most appropriate type of resistance must be chosen, although the value of the resistance is the same regardless of its type; Their properties vary and their performance is affected in some circuits depending on their type.

Principle of electrical resistance

It is known that when an electrical voltage is applied between the two ends of a conducting material, an electric current will arise in it resulting from the movement of free electrons present in the structure of the conducting material from the point with low voltage to the point with high voltage, where during their movement they collide with the atoms of the material that prevent them from moving. This is called electrical resistance.

Since the tension applied to the conductive material is directly proportional to the current passing through it, the resistance can be considered the ratio of the applied tension to the current, and accordingly the law of electrical resistance was formulated, which is measured by a unit called an ohm, symbolized by omega  Ω .

R=V/I

• R : resistance.
• V : tension.
• I  : current intensity.

Types of electrical resistors 1

Factors affecting electrical resistances

The electrical resistance in the circuit is used to reduce the electrical current passing through it, divide the voltage, and modify the signals. Therefore, the value of the resistance must be chosen accurately so that it fulfills its required purpose, and all that must be done is to connect the resistance within the circuit.

A resistor generally consists of a conductive wire wound over an insulating material, often ceramic. The number of turns and cross-section of the wire governs the value of the resistance; As the number of turns increases and the wire cross-section decreases, the resistance value increases and vice versa. That is, electrons will have more difficulty moving if the wire is longer or has a smaller cross-section.

In addition to this is the effect of the material it is made of, as materials that conduct electrical current show less resistance than insulating materials, and this is symbolized by the specific resistance of the material and is measured in ohms.

Effect of temperature on electrical resistance

Although resistance changes depending on the length of the conductor and its cross-sectional area, the role of temperature and its effect on the resistance value cannot be overlooked. As temperatures change, the conductive material expands or contracts, as most metals are affected by heat and thus their dimensions change.

But that does not mean that it is the main reason for the change in the resistance value, because the matter is largely related to the specific resistance of the conducting material. When the temperature rises, the vibration of the atoms and ions of the conducting material increases, which constitutes a greater obstacle to the movement of electrons, and thus increases the electrical resistance.

This can be summarized by saying that the relationship between temperature and resistance is a direct relationship. The higher the temperature, the greater the resistance, and the lower the temperature, the lower the resistance. Here it is necessary to point out the possibility of reducing resistance to zero, and it is then called absolute conductivity.

Methods of connecting resistors

Resistors can sometimes be connected in series or parallel to achieve a specific resistance value required in a circuit.

Connect the resistors in series

The resistors are connected in series so that the current passing through all the resistors is equal, while the total (equivalent) resistance is the sum of the value of the resistors connected in series. Therefore, if one of the resistors stops working, the entire circuit stops.

Connecting resistors in parallel

Here, one end of the resistors is connected to one point and the other end to another single point, so that a single voltage is applied to all the resistors, while the current passing through the circuit is distributed among the resistors. As for the total resistance, it is calculated from the sum of the reciprocal of the value of each of the resistors connected in parallel.