Joule effect


The Joule effect is a term commonly used to refer to any of the different physical effects discovered or characterized by the English physicist James Prescott Joule . These physical effects are not the same, but they are all occasionally referred to in the literature as the “Joule effect” or “Joule law . ” These physical effects include: Joule’s First Law, a physical law that expresses the relationship between generated heat and current flowing through a conductor . Joule’s second law which states that the internal energy of a gasideal is independent of its volume and pressure , depending only on its temperature .

  • Unit:  Joules
  • Symbol: E
  • Formula:  E = R · I² · t

What is the Joule effect?

It is the effect that occurs when in a conductor where electricity circulates , part of the kinetic energy that the electrons have is transformed into heat by the collision of the electrons with the molecules of the conductor.

  • What is the Joule effect?
  • Joule effect explained
  • Formula
  • Applications of the Joule effect
  • Examples

What is the Joule effect?

The Joule effect was discovered by James Prescott Joule and is also known by the name of resistive or ohmic heating , which describes the process in which the energy in an electric current can be transformed into heat as it flows through a resistance.


In particular, when electrical current flows through a solid or liquid with finite conductivity , the electrical energy is converted into heat through resistive losses in the material. Heat is generated on the microscale when conduction electrons transfer energy to conductor atoms through collisions .

The transfer of energy is carried out at the level of the molecules : the interaction of the electron current with the ions or with the atoms of the part of the energy conductor remains in the latter. The thermal effect is obtained by the cables with the faster movement of the conductive particles and their internal energy increases and is transformed into heat .

Joule effect explained

To understand how the Joule effect works, we must begin by explaining what heat is . Heat is the release of energy by a system that originates as a consequence of movement and the particles that compose it.

The Joule effect occurs when there is the release of heat stimulated by the movement of electrons , or what we normally know, the electric current through a given material. In addition, the joule effect will depend on several aspects, which are:

  • The intensity of current : refers to the number of electrons per unit of time . The lower the resistance and the greater the potential difference , the more electrons will be moving in a unit of time.
    Resistance : it is the opposition of an element to the passage of electrons through it. The higher the resistance, the greater the number of obstacles in the electron path.
  • The difference in potential or voltage : the atoms are responsible for attracting electrons from the positive to the negative pole, generating movement .
  • Time : the longer the time elapses, the amount of heat that has been generated increases and for this reason it also influences .
  • Power : refers to the influence of resistance , intensity and potential difference of a circuit.


In Joule’s law or Joule effect, thermal energy is represented by the letter E (in Joules or Joules) and this thermal energy is dissipated by an electrical resistance conductor , which is represented by the letter R (ohm) and that it is traversed by a current of intensity I (measured in amperes) for a time t. This explanation can be represented by the following formula:

E = RI²t

Thermal energy or in other words heat, represented by the letter E will depend on 3 different factors that are the following:

  • The intensity I of the current (which is considered the most important factor since it is squared).
  • The time t during which the current flows.
  • Resistance R of the conductor.

Applications of the Joule effect

In practical life, the joule effect is applied in the different electrical appliances that we generally use in our homes with electric heaters that take advantage of this calorific effect. This principle also applies to the incandescent lamp which works when the filament raised to a very high temperature emits light.

It can also be applied to hair dryers, for example, since they have a series of resistors inside that heat up little by little while the electric current passes, causing the air that manages to come out of them. be hot.


Some examples of the joule effect can be found in:

An ordinary light bulb.

  • Heating devices.
  • Fuse in the apartment.
  • Electric stove heaters.
  • The arc that is used for the welding of metal structures.

Leave a Comment