Type of Materials


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There are three types of materials that are observed in electricity given as follows:

(i) Conductors: These are the materials in which electric charges move freely. Most of the conductors are metals like copper, aluminium and steel. Conductors are materials that obey Ohm's law and have very low resistance. They can therefore carry electric currents from place to place without dissipating a lot of power. As a result, metals are useful as connecting wires to carry electrical signals from place to place. Modern resistors are also made of conductor materials. However, they use very thin pieces of conductor which don't pass current too easily.

(ii) Insulators: These are the materials in which electric charges cannot move freely or in other words, these materials do not allow electric charges to flow. Glass, most polymers (plastics), rubber and wood are all examples of insulators. They are useful for jobs like coating electric wires to prevent them from 'shorting together' or giving you a shock. Silk and cotton in dry condition are also good insulators and some of the mains wiring in very old houses once used them but by modern standards this was pretty dangerous since you could get a shock when wet. Insulators are also very useful to fill the 'gap' in between the metal plates of a capacitor. Very old capacitors (and some modern radio ones) use air gaps since air is a good insulator. Modern insulators like PVC (Poly Vinyl Chloride) are much better and safer.

(iii) Semiconductors: The semiconductors are the third class of materials and their electrical properties are somewhere between those of insulators and those of conductors. A semiconductor will carry electric current, but not as easily as a normal conductor. All the transistors, diodes, integrated circuits, etc. used in modern electronics are built using a range of semiconductors. Silicon and germanium are well known examples of semiconductors commonly used in the fabrication of variety of electronic devices, such as transistors and light-emitting diodes. The electrical properties of semiconductors can be changed over many orders of magnitude by the addition of controlled amounts of certain atoms to the materials.

Consider a conductor placed in an electric field in a static condition. In this case, the conductor is at rest and thus there is no change in the number of lines of force linked with it per unit area (equal to the flux). Since, there is no rate of change in flux; there will be no flow of electric current in it.

When a conductor is placed in an electric field so that it is moved in the electric field the flux linked with the conductor per unit area per unit time will change. Then there will be an induction of electric current. Hence, there will be a flow of current inside the conductor.