What is Electrical Resistance – An Overview

The materials are categorized into two different types namely conductors and insulators. A conductor allows the flow of current whereas an insulator doesn’t. So the conductor materials should require the resistor components in their structure. Every electrical device has an internal circuit and the working of this circuit mainly depends on the proper input voltage, grounding connections, and dissipated heat should be minimum. From all these one of the important points to be considered here is the circuit resistance. In any electrical circuit design, the resistors play a key role by helping the circuit to maintain the proper voltage and current. By the end of this article, we will study what is electrical resistance, Unit of Resistance, resistance in electricity, electrical resistance and conductance, formula and examples.

What is Electrical Resistance?

A resistor is a two-terminal electrical component. The primary property of a resistor is to oppose the electrical flow or reduces the current flow. Because sometimes it allows high current flow so it can damage the device. Every electrical device requires input voltage to starts working as the device getting the sufficient input voltage; this voltage helps to gain sufficient energy for electrons to flow. This results in the generation of current in the device. Every device has some limitations like maximum input power, maximum current level. So when the device gets more current than their limit, it’s going to be damage. To avoid this we should limit the current by using a resistor.

While designing the circuit for a device, manufacturers know the electrical limitations for the device. As per the requirement, they place few resistors in the circuit to maintain the sufficient current. Even though, the excess current can be prevented/avoided by the resistors. In this way, the resistors play an important role in the circuits and for devices.

Ohm’s Law

A German scientist George Simon Ohm proposed a theorem that shows the relation between voltage, current, and resistor. By this theorem, we can find how much resistance value is required for a circuit with the knowing value of voltage and current. And also we can find the value of voltage, resistor and current values by the theorem ohm’s law.

Ohm's Law
Ohm’s Law

Ohm’s law states that the current through a conducting material/device between ranges is directly proportional to the voltage across the same range. Or in another way, the generated current through a conducting device is directly proportional to its input voltage. The unit of resistance is ohms and denoted by symbol Ω. The below equation shows the electrical resistance formula.

                                V = I * R

From above ohm’s law, we can able to find the current and resistance value also.

                                I = V/R

                                R = V/I

How Does a Resistor Work?

Here the interesting question comes, how the resistor works and how it’s going to prevent the electrical flow? The answer is it depends on its structure and design. If we clearly observe the design of the resistor we come to know that, it is short, it has color stripes on the top & it has two connections, by using this we can connect any one of the sides to the circuit. The below figure indicates how a resistor looks like.


Inside a Resistor – if you break & open any one side of the resistor colored strip point, you can observe an insulated copper rod which is covered with copper wire around it. The count of copper wire turns can be decided by the resistor’s resistance value. If the resistor has more copper turns in a thin form then such resistors have higher resistance. If the resistor having low copper turns then such structured resistors have lower resistance value. Those lower resistance valued resistors are suitable for the mini circuit or smaller applications or devices. This is the secrete about how the resistors are having a different resistance value. The next section will know how the size of the resistor affecting its resistance value.

Does the Size of the Resistor Affect the Electrical Resistance Value?

The size of the resistor also can decide the resistance value. How it means according to George Ohm, also proved a relation between length and resistor and material (from which material the resistor was made). According to his statement, the equation is

                                           R = ρ * L / A


R = Resistance

Ρ = Resistivity of the material

L = Length

A = Area

As we know the materials are classified into two types. They are conductors and insulators. In a conducting material, the length plays an important role while maintaining the resistance value. In a conducting material if the length of the wire is so long then it has a large number of free electrons in it. So these electrons will get enough kinetic energy when they got sufficient input voltage. And these electrons get a collision with other positive ions.

Therefore, a longer conductor offers more resistance than the shorter conductor/wire. If the length of the wire increases, then its resistance also increases as per the above statement. But if the area of the material increases, the resistance is decreased. Here the resistance and area of the material are having inversely proportional to each other. And the type of material also can violate the resistance value. Like temperature can able to change the resistance value.

  • If the devices are positive temperature coefficients, then the resistance increases with the increment of the temperature.
  • If the resistors are used in series form in the circuit then such a circuit is called as voltage divider network.
  • When the resistors are used in parallel form in the circuit then such a circuit is called the current dividing network.
  • Resistors’ value can be known by the color-coding technique. There are 3 band resistors and four-band resistors are widely used in the circuits. All resistors are having a color strip on their top. These colors help to find their resistance value. The available colors on the resistors are Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Grey and White. On each resistor, the last colored strip is indicating the tolerance value. There are four colors available on the last strip of the resistors. They are Brown, Red, Gold, and Silver.
  • Tolerance value for Brown is ±1%, Red ±2%, Gold ±5%, Silver ±10%.

Every electrical device requires electricity to work properly. The flow of electrons can be opposed by electrical resistance. Resistors are having two terminals and their resistance can be dependent on the number of copper turns inside of the resistor. We have seen how the resistor can oppose the flow of electrons. By the color-coding technique, we can find the resistor resistance value. There are three band and four-band resistors are used in the electrical circuits.