Electrical Resistance. Concept, formula and types

08/05/2026

The online electrical resistance simulations on this page will help you to better understand this important quality of materials and to know its relationship with other electrical quantities such as electrical current and voltage.

This Thematic Unit is part of our Physics collection

Conductivity

Physical property that measures the ability of a substance to allow the passage of electricity or heat.

Electrical Resistance

Measure of the opposition that a material presents to the flow of electrical current. The SI unit of measurement is the Ohm (Ω).

Joule Effect

Phenomenon by which electrical energy is transformed into heat as a current passes through a material with resistance (P = I² · R).

Pouillet’s Law

Formula stating that the resistance of a conductor is proportional to its length and inversely proportional to its cross-sectional area: R = ρ · l / A.

Resistivity

Intrinsic property of a material indicating how much resistance it offers, regardless of its shape or size.

Temperature Coefficient

Factor indicating how the resistance of a material changes with temperature, generally increasing in metals.

Concept of electrical resistance

Electrical resistance is a property of materials that opposes the flow of electric current through them. It is measured in ohms (Ω) and is symbolized by the letter “R”.

Factors of electrical resistance

Electrical resistance depends on several factors, such as the type of material, its length, its cross-sectional area and its temperature. Materials that exhibit high resistivity, such as tungsten or nichrome (nickel-chromium alloy), are commonly used in the manufacture of resistors.

Formula of electrical resistance. Ohm’s law

The formula for electrical resistance is obtained from Ohm’s law, which states that the current (I) flowing through a conductor is directly proportional to the voltage (V) applied and inversely proportional to the resistance (R) of the conductor. The relationship is expressed by the formula:

I = V / R

Where

I is the current in amperes (A)

V is the voltage in volts (V)

R is the resistance in ohms (Ω)

Applications of electrical resistance

Resistors are used in a wide variety of electrical and electronic applications to limit current, control power and divide voltage. They are also used in circuits to protect sensitive components by limiting the amount of current flowing through them.

It is important to note that resistors have a limited capacity to dissipate energy in the form of heat. If their capacity is exceeded, they can be damaged or even burned out. Therefore, it is essential to select a suitable resistor for the specific application and to consider the maximum power it can dissipate without overheating.

Types of electrical resistance

There are different types of resistors, such as fixed resistors and variable resistors (potentiometers and rheostats), which allow their resistance value to be adjusted. There are also special resistors, such as temperature-sensitive resistors (thermistors) and light-dependent resistors (photocells or LDRs).

Conductivity

Physical property that measures the ability of a substance to allow the passage of electricity or heat.

Electrical Resistance

Measure of the opposition that a material presents to the flow of electrical current. The SI unit of measurement is the Ohm (Ω).

Joule Effect

Phenomenon by which electrical energy is transformed into heat as a current passes through a material with resistance (P = I² · R).

Pouillet’s Law

Formula stating that the resistance of a conductor is proportional to its length and inversely proportional to its cross-sectional area: R = ρ · l / A.

Resistivity

Intrinsic property of a material indicating how much resistance it offers, regardless of its shape or size.

Temperature Coefficient

Factor indicating how the resistance of a material changes with temperature, generally increasing in metals.

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

Simulations of electrical resistance

Electrical resistance of a wire

Observe the changes in the equation and the wire as you play with resistivity, length and area.

Electrical Resistance Lab

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1831

–

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Test your knowledge

What is electrical resistance, and on which factors does it depend according to the physics of materials?

Electrical resistance is the property of a material that opposes the flow of electric current and manifests as a loss of energy in the form of heat, and it depends directly on the material’s resistivity, the length of the conductor, its cross‑sectional area, and its temperature, so materials with high resistivity such as nichrome or tungsten show large resistance values, while conductors like copper or silver offer much less opposition, and in addition a longer or thinner conductor increases resistance because electrons must travel through a narrower path with more internal collisions, which explains why both the geometry and the intrinsic nature of the material so clearly determine its electrical behavior.

How is resistance related to Ohm’s law, and what implications does this relationship have for circuit analysis?

Resistance appears in Ohm’s law as the quantity that links the applied voltage and the resulting current through the expression (I = V / R), which means that for an ohmic material the current increases proportionally with voltage as long as resistance remains constant, and this relationship allows us to predict circuit behavior, size components correctly, calculate voltage drops, and determine whether a device can dissipate the associated power without overheating, since a resistance that is too low would cause excessive currents and one that is too high would limit the circuit’s operation, making Ohm’s law the quantitative foundation for designing and understanding electrical systems.

Why do some materials let current pass so easily while others slow it down a lot? It feels like some are “friendly” and others aren’t.

The difference comes from how electrons move inside the material, because in metals electrons are very free and can travel with few obstacles, while in materials with high resistivity electrons collide constantly with atoms and internal defects, which slows their motion and makes current flow with more difficulty, so it’s not that some materials are “friendly,” but that their internal structure either helps or hinders the movement of electrons.

Why does a resistor get so hot if it’s just “slowing down” the current? It seems strange that this ends up producing heat.

When current passes through a resistor, electrons collide repeatedly with the atoms of the material and transfer part of their energy in each collision, and that lost energy becomes heat, which is why a resistor that is limiting current can heat up quite a lot, and if it exceeds the power it can safely dissipate it ends up being damaged or even burning out, which is why choosing a resistor with the right power rating is essential in any circuit.

Why are there so many different types of resistors? Sometimes it feels like they all do the same thing.

Although all resistors are used to limit current or adjust voltage, there are fixed, variable, temperature‑dependent, and light‑dependent resistors because each one is designed for a specific function, so a potentiometer allows manual adjustment of a value, a thermistor changes its resistance with temperature, and an LDR responds to light, meaning there aren’t different types “just because,” but because each application needs a particular behavior that a normal resistor couldn’t provide.