Describe process that causes electrical energy to be transformed into thermal energy as a current flows in a light bulb?

Answer 1

All electrically conductive materials have an inherent resistance ( i.e a property which tends to oppose the flow of an electrical current ) which is a physical characteristic depending on the type of material composition , the cross sectional area & length over which the electrical current is flowing & the working temperature.

This resistance property has both positive & negative implications for electrical applications, which is detailed below.

There are also some deviant materials which are briefly outlined here for comparative infomation.

Some of these special materials at very low temperatures will Not have any resistance at all. They are called Superconductors & are used in speciallised applications which presently are Not in common use.

Then there are certain materials which exhibit large changes ( either increase or decrease in resistance for small changes in temperature.) These materials are Not used in normal electrical devices but find applications in temperature sensing & controlling applications.

As regards materials which are used as wires to conduct the electrical energy from one place to another, they have to exhibit as low resistance as possible to reduce energy loss in use. Typically copper or aluminium are used for such applications for which high resistance is a negative point.

The Most important point to note is that energy loss in any electrical circuit typically results in generation of heat, which is then lost to the surroundings which may is undesirable in most applications.

However when the electrical energy is to be required to put in actual use in a heater or a lamp, for such applications a calculated resistance is deliberately utilised to control the flow of electrical current & thereby the required heat & temperature. Here high resistance is a positive point. Typically materials like Nichrome ( for heaters ), Tungsten for Incandescent lamps are used. In such applications deliberate use of the heating property in a resistive electrical circuit is utilised

The resistance value is carefully calculated as per the heat required , the supply voltage & other technical factors which will ultimately determine the stable operating temperature rise in such applications.

For an incandescent lamp, another physical property , which is the emission of different wavelenghts of electromagnetic radiation depending on the temperature & type of material is utilised.

The electrical energy flowing through the resistive part of the lamp increases the filament temperature to such an extant that infrared or visible wavelengths of light are emitted. This is akin to heating a piece of iron in a furnace. The iron first glows dim red ( infrared ), then increasingly grows brighter from cherry red to yellowish white as the temperature rises.

In a lamp as the filament is a very thin tungsten wire glowing white hot, it will burn out in presence of oxygen & /or other undesirable gases. Therefore a vaccum is created in the glass bulb to prevent burnout. Modern High Power lamps use a small quantity mixture of Halogen family gasses to improve the performance & reduce the overall size of such lamps.