At atomic level, conduction is due to collisions between the atoms or molecules of the material through which heat flows. Collisions between atoms / molecules cause an exchange of kinetic energy between molecules. Less energetic molecules gain energy by colliding with more energetic molecules.
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The net result is that heat flows from higher temperature region to lower temperature region of he medium.If we hold one end of a long metal rod in hand and introduce the other end into a flame, the temperature of the metal end in our hand increases.
The energy reaches the hand through conduction. Let us try to understand the is mechanism.Before the rod is introduced into the flame, the atoms were vibrating about their equilibrium positions with certain amplitudes. Upon insertion of one end of the rod into the flame, energy is provided to the rod at the other end. The atoms at the end of the rod in the flame begin to vibrate with larger and larger amplitudes. These atoms collide with their adjacent atoms and transfer some of their energy to them.
Gradually metal atoms away from the flame receive energy and their amplitude of vibration increases. Slowly atoms at the end of the rod in our hand are affected and the amplitude of their vibrations increase resulting in rise in temperature of that end Process of conduction:Conduction of heat can take place in liquids and gases also.Liquids conduct heat with less ease than solids, because average distance between the atoms/molecules is relatively greater than that in solids and the forces between the atoms are weaker.
Gases are even less efficient conductors than liquids as the atoms / molecules have to travel greater distances before they collide.Conduction occurs between objects that are in contact. Conduction of heat takes place between the objects till they attain the state of thermal equilibrium when the average kinetic energies of the atoms in the two objects are equal and the two objects are at the same temperature.
Rate of conduction:The rate of conduction (the rate of energy transfer) depends on the nature of the material medium. For example, we can hold a piece of asbestos in a flame indefinitely because very little energy is conducted through it. Metals are good thermal conductors for they have free electrons in abound, freely moving through the metal and transporting energy from one region to another in it. In metals, such a copper, conduction takes place due to vibrations of atoms and also due to motion of free electrons. Material such as asbestos, cork, fiber glass, paper, wood, ebonite, glass, paper are poor conductors of heat. These are called bad conductors. Mercury being a liquid metal is a good conductor.