Conduction Definition in Physics

Conduction: How Energy Moves Through an Object

A heated metal bar displays thermal conduction.
A heated metal bar displays thermal conduction. Dave King/Getty Images

Conduction Definition

Conduction is the transfer of energy by the movement of particles that are in contact with each other. The word "conduction" is often used to describe three different kinds of behavior, defined by the type of energy being transferred:

  • Heat Conduction (or Thermal Conduction) - Heat conduction is a heat transfer through direct contact within or between solid objects, such as when you touch the handle of a hot metal skillet. 
  • Electrical Conduction - The conduction of electrical current, such as through the wires in your house.
  • Sound Conduction (or Acoustic Conduction) - The conduction of sound waves, such as feeling the vibrations of music through a wall.

A material which provides good conduction is called a conductor, while materials that provide poor conduction are called insulators.

Heat Conduction

Heat conduction can be understood, on the atomic level, as particles physically transferring the heat energy as they come in physical contact with neighboring particles. This is similar to the explanation of heat by the kinetic theory of gases, though transfer of heat within a gas or liquid is usually referred to as convection. The rate of heat transferred over time is called the heat current, and it is determined by the thermal conductivity of the material, a quantity that indicates the ease with which heat conducts within a material.

Example: If an iron bar is heated on one end, as shown in the image, the heat is understood physically as the vibration of the individual iron atoms within the bars. The atoms on the cooler side of the bar vibrate with less energy. As the energetic particles vibrate, they come in contact with adjacent iron atoms and impart some of their energy to those other iron atoms.

Over time, the hot end of the bar loses energy and the cool end of the bar gains energy, until the entire bar is the same temperature. This is a state known as thermal equilibrium.

In considering heat transfer, though, the above example is missing one important point: the iron bar is not an isolated system. In other words, not all of the energy from the heated iron atom is transferred by conduction into the adjacent iron atoms. Unless it's being held suspended by an insulator in a vacuum chamber, the iron bar is in physical contact with a table or anvil or other object, and is also in physical contact with the air. As air particles come in contact with the bar, they too will gain energy and carry it away from the bar (though slowly, because the thermal conductivity of unmoving air is very small). The bar is also so hot that it is glowing, which means that it is radiating heat energy in the form of light. This is another way that the vibrating atoms are losing energy. Eventually, the bar would reach thermal equilibrium with the surrounding air, not merely within itself.

Electrical Conduction

Electrical conduction happens when a material allows an electrical current to pass through it.

This is based on the physical structure of how the electrons are bound within the material and how easily an atom releases one or more of its outer electrons to the neighboring atoms. It is possible to measure the amount that a material inhibits the conduction of an electrical current, called the electrical resistance.

Certain materials, when cooled to nearly absolute zero, exhibit the property that they lose all electrical resistance and allow electrical current to flow through them with no loss of energy. These materials are called superconductors.

Sound Conduction

Sound is physically created by vibrations, so it is perhaps the most obvious example of induction. A sound causes the atoms within a material, liquid, or gas to vibrate and transmit, or conduct, the sound through the material. A sonic insulator is a material where the individual atoms do not easily vibrate, making them ideal for use in soundproofing.

 

Conduction Is Also Known As

thermal conduction, electrical conduction, acoustical conduction, head conduction, sound conduction

Edited by Anne Marie Helmenstine, Ph.D.

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Jones, Andrew Zimmerman. "Conduction Definition in Physics." ThoughtCo, Oct. 15, 2016, thoughtco.com/conduction-2699115. Jones, Andrew Zimmerman. (2016, October 15). Conduction Definition in Physics. Retrieved from https://www.thoughtco.com/conduction-2699115 Jones, Andrew Zimmerman. "Conduction Definition in Physics." ThoughtCo. https://www.thoughtco.com/conduction-2699115 (accessed December 15, 2017).