S2-HEAT RADIATION

 

By PragyanSharma Polavarapu

Heat and light are the most familiar forms of energy man used from beginning of time. We can see power of heat in the wild fires of forests and in the heat of white-hot bars of iron rolling out of a steel mill. We see that a sudden flood of light fills the dark room when we switch on the electric bulb. We can compare the infinite light and heat coming from Sun with the darkness of night . We now know that “heat” and “light” are terrific energies. Let us restrict now to study of Heat energy which is a radiation, being one kind of electro-magnetic radiation.

The burning of a piece of wood or piece of paper or an oil-soaked cloth is explained by modern science as follows:

(a) The flame is the visible area of an “exothermic” chemical reaction in which billions and billions of molecules of hydrocarbons are reacting with oxygen molecules contained in air. Much heat is released during the reaction appearing in the shape of a big visible flame. The “chemical bonds” in all the hydrocarbon molecules—whether in wood, paper, cloth or oil –are broken and water vapor and carbon dioxide are formed and much heat energy is released in addition to the bright light of the flame.

Flame is the vast area of chemical reaction where great “heat” energy at temperature between 500 degrees to 1000 degrees centigrade is released making reaction gases glow with visible “light” energy.

(b)When a combustible substance is being burnt or when a metal block is being heated , billions upon billions of “heat energy packets” or “ heat quanta” are emitted by the very hot and highly excited atoms of gases in the flame which are billions and billions and billions in number. The heat energy quanta thus emitted are absorbed by orbiting electrons inside the atoms of all the cool objects nearby. The electrons loaded with energy quanta are pushed to inner orbits inside every atom in the cold substance.

( c )When heat energy stops coming from outside, the electrons ( in atoms of cool substances nearby) release energy quanta to outside of the atom and return back to their original “zero energy level” orbits. The quanta (energy packets) released to outside world may be different from the quanta which entered inside atom because some energy is absorbed by the atom . As a result new photons ( new quanta) may be emitted by the electrons orbiting inside atoms.

(d) What we experience as heat energy, light rays, ultra violet rays, X-radiation etc are the billions and trillions of energy quanta (packets of energy wavelets) released by the electrons orbiting inside the billions and trillions of atoms. All these ideas in advanced modern physics came only after research in physics in early part of 20th century about electrons and other sun-atomic particles took place. However let us go back to the old classical physics of 200 or 300 years back .

Chemical Reaction

In some cases when two or more different pure chemical substances are intimately mixed , for example, by adding to a large quantity of water in a glass vessel a “chemical reaction” may occur. This means old reacting substances(reactants) disappear and entirely new substances(resultants) appear. This is explained as below.

The billions upon billions of molecules break and the smaller unbreakable particles (atoms) come out . The atoms are absolutely unbreakable and can only form new groups i.e. new molecules. Chemical reaction means the combining of atoms into new groups or new molecules. Some times when we mix two or more different pure chemicals in water and heat the mixture , a reaction like quick appearance of fast moving little solid grains in the vessel or minute bubbles or evolving of vapors etc will occur . This means that atoms contained in a certain reactant are showing greater affinity to another type of atoms in another reacting substance nearby. We should remember that atoms are unbreakable minute particles of matter. New chemical substances i.e. billions upon billions of new molecules will form. Some of these new chemicals dissolve in water and some are insoluble .

It is like present friends groups (existing molecules) separating and new friends groups (new molecules) forming. All are participating in a locked campus and so total number of people inside does not changes. This is the same as “Law of Conservation of Mass” in chemical reactions . The law states that total number of atoms before reaction is equal to total number of atoms after reaction. Atoms can neither be created nor destroyed.

“Precipitates” like colored curd grains may appear in the liquid and settle down. Sometimes gases may evolve. In some cases extra heat may be generated in the reaction. In some reactions strong smelling gases may evolve or new chemicals of different colors may appear.