Joule effect

Joule effect If an electric current flows through a conductor, part of the kinetic energy of the electrons is transformed into heat due to the collision that the electrons undergo with the molecules of the conductor through which they circulate, raising its temperature.


Solids generally have a crystalline structure, with the atoms or molecules occupying the vertices of the unit cells, and sometimes also the center of the cell or its faces.

The crystalline being subjected to a potential difference, the electrons are driven by the electric field through the solid, having to pass through the intricate network of atoms that form it. On their way, the electrons collide with these atoms, losing part of their kinetic energy (velocity), which is transferred in the form of heat.

This effect was defined as follows: “The amount of heat energy produced by an electric current depends directly on the square of the intensity of the current, the time it circulates through the conductor and the resistance it opposes to the passage of the current. ” Mathematically:

Q = I2 • R • t, ​​where

Q = heat energy produced by the current expressed in Joule I = intensity of the current flowing

R = electrical resistance of the conductor

t = time

This effect is based on the operation of different household appliances such as ovens, toasters, electric heaters, and some devices used industrially as welders, etc. in which the useful effect sought is precisely the heat given off by the conductor through the passage of current.

In many applications this effect is unwanted and is the reason that electrical and electronic devices (such as the computer you are reading this from) need a fan that dissipates the heat generated and prevents excessive heating of the different devices.

Carrying out a new analysis of the Joule effect , it is known that when the electric current circulates through a conductor, it encounters a difficulty that depends on each material and which is what we call electrical resistance, this produces losses in voltage and power, which in turn Once they lead to heating of the conductor, which causes a loss of electrical energy, which is transformed into heat, these losses are valued using the following expression:

Ep = Pp * t


Pp = lost power

t = time in seconds.

This effect is exploited in heating devices, where these losses are transformed into heat energy, which is expressed by the letter Q, and is measured in calories.

Specific heat . Amount of heat that is communicated to a body to raise the temperature by one degree, one gram of the total mass. Specific heat values ​​for some materials are listed below. The heat energy as a function of the specific heat and the temperature variation is expressed as follows:

Q = Ce * m * ΔT


Q = Heat energy in calories

Ce = specific heat Cal / g * ºC

m = body mass in grams

Δt = temperature increase in degrees celsius.


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