Some of the most important Physics Topics include energy, motion, and force.
Conductors And Insulators : An Overview
Electric charge cannot flow through all substances with equal ease. According to the ability of charge to move through the materials, they are classified into two major groups—
- conductor and
- insulator or non-conductor.
Conductor: Materials through which charge can move easily are called conductors. If some charge is given to any part of a conductor, it will spread all over the body of the conductor. Generally all metals are conductors of varying degrees. Among them silver, copper, aluminium rank higher. Earth, human body, gas carbon, graphite, mercury, etc., are also conductors. Acid, alkali and aqueous solution of salts also conduct electricity. Generally, no material is a perfect conductor.
Insulator or non-conductor: Materials through which charge cannot move are called insulators or non-conductors. If any part of an insulator is charged, charges remain confined to that part of the insulator and do not spread all over the body. Dry air, glass, rubber, ebonite, mica, silk, paraffin, bakelite, etc., are insulators. Remember that generally no material can be said to be a perfect insulator.
Besides conductors and insulators, there is a third kind of mate-rials called semiconductors, which are neither good conductors nor good insulators. Selenium, germanium, silicon, etc., are semiconductors. They are widely used in electronic circuit elements like transistors, integrated circuits etc.
Nowadays a few substances can be made to behave as almost perfect conductors at very low temperature. These are called superconductors. Aluminium acts as a superconductor at -272 °C . Dry air is a good insulator. But charge can flow through moist air. Hence experiments on statical electricity cannot be con-ducted satisfactorily in rainy season.
In electricity supply system, the transmission wires are joined through porcelain pots, which are non-conductors. But if the wires were directly connected to the electric post, electricity would have been grounded instantly and there would be a huge transmission loss, and if someone touches the post, there would be a chance of getting shock. In a laboratory connecting wires used for different electrical experiments are wrapped with rubber, silk or cotton to reduce the chance of short circuit. These are called insulated wires.
Pure water is a non-conductor, but various types of salts, bases and acids are dissolved in natural water which makes it a fairly good conductor.
Conductors and insulators on the basis of electronic theory: The electrons of the outermost orbits of the atoms of a conductor are very loosely bound to the nucleus and move freely from one atom to another. These electrons are called free electrons. These free electrons carry electricity from one place to another throughout the conductor. Metals are good conductors due to the presence of free electrons in them. In insulators or nonconductors electrons are tightly bound to the nucleus—they are not free electrons. So electricity cannot flow through them.
Charging By Conduction
A conductor with a non-conducting handle is called an insulated conductor. Charges given to this conductor cannot go elsewhere and it becomes a charged conductor. If an uncharged insulated conductor be brought in contact with such a charged insulated conductor, some charges cross over to the uncharged conductor, which becomes charged. This process of charging a conductor by direct contact with a charged body is known as charging by conduction. It can be explained on the basis of electronic theory.
Explanation of charging by conduction on the basis of free electronic theory: Suppose a body is negatively charged. So it has excess electrons. When this charged body comes in contact with an uncharged conductor, a few electrons from the charged body move into the conductor.
As the conductor now has excess electrons, it becomes negatively charged. If the body is positively charged initially and is touched with an uncharged conductor, a few electrons of the uncharged conductor move to the charged body due to attraction by the positive charge. As the conductor now has a deficit of electrons, it becomes positively charged. Note that, in both cases, the initial amount of charge in the charged body is shared between two bodies due to conduction. As a result, the strength of charge in the first body is reduced to some extent.