ABSTRACT
According to the modern or dynamical Theory of heat: Heat a form of energy. The molecules of a substance are in parallel motion. The mean Kinetic energy per molecules of the substance is proportional to its absolute temperature. In description of heat, a molecule may consist of one or two or many atom depending upon the nature of the gas. The force of attraction between the molecules of a perfect gas is negligible. The atom in a molecules vibrate with respect to one another, consequently a molecules has vibration energy. The whole molecules may rotate about one or more axes, so it can have “notational energy”. A molecule has “translational energy” due to its motion, thus kinetic energy of a molecule is “the sum of its translational, rotational and vibrational energies. Summarily heat energy given to a substance e is used in increasing its internal energy. Increase in internal energy cause increase in Kinetic energy or potential energy or increase in both the energies. Due to increase in Kinetic energy of a molecules, its translational, vibrational or rotational energy may increase. In a nut shell “heat transfer is the science which deal with the rate of bodies called the Source aims receiver KERN, [2006:1]