Fundamental concepts about electricity for learners

Electricity produced by friction between two dissimilar objects is known as static electricity. For example, if a glass rod is rubbed with silk, the rod requires a positive charge and the silk has an equal negative charge.

Conductors

Substances that can conduct electrical charges are called conductors. All metals conduct electricity because they have a large number of free electrons.

Insulators

Insulators have no free electrons and do not conduct electrical charges. Most non-metals are insulators. For example wood, glass, rubber, pure water.

Superconductors

The resistance of metal to the flow of current reduces with decreasing temperature. At temperatures near absolute zero which means -273⁰ C metals have almost zero resistance and become superconductors.

Certain ceramics can be made to behave as superconductors at relatively high temperatures of above 100k.

Semiconductors

Certain materials have electrical resistivity intermediate between those of conductors and insulators. These materials are termed as semiconductors. For example, Silicon and Germanium are the semiconductor materials.

They are good insulators in their pure crystalline form, but their conductivity increases if small amounts of impurities are added to them. After the addition of impurities, they become n-type and p-type semiconductors.

Lightning conductor

Lightning conductors are used to protect tall buildings from lightning damage. Here a thick copper strip is fixed to an outside wall of the building. The upper end of the strip is in the form of several sharp spikes reaching above the highest part of the building. The lower end is connected to a copper plate buried in the earth.

When clouds charged positively or negatively come near the spitted conductor, the clouds induce an opposite charge on them that is streamed off by the points.

In the process, the clouds get discharged and an intense spark discharge, which might otherwise pass through the building causing heavy damage, is averted.

Magnetic effect of current

A current-carrying wire has a magnetic field around it. Electromagnets are produced in this way. Strong electromagnets find a lot of applications in industry for lifting and transporting steel plates. They are used in electric bells, and telephone receivers.

The heating effect of the current

When a charge moves in a conductor, it does work, which results in heating the conductor.

If the resistance of a wire is R ohms and the current flowing through it is I ampere, the heat produced per second in the wire is I² R Joules.

The heating effect of current is used in geysers, electric irons, toasters, ovens, room heaters and so on. 

Some facts about electricity

Ic chips for computers are usually made of silicon.

Semiconductor is made of silicon and germanium.

Soft iron would be most suitable for making an electromagnet.

Nichrome wire is used as a heating element in many appliances. Because it has high resistivity and resists oxidation in air when red hot.

Energy conversions in a loudspeaker are electrical to mechanical to sound.

Energy conversion takes place in a microphone from sound to mechanical to electrical.

A transformer is a device for stepping up AC voltage.

The advantage of AC over DC is that it can be transmitted over long distances with minimum power loss.

The material used for a fuse wire should have a low melting point.

One should not connect several electrical appliances to the same point socket. Because of this can damage the domestic wiring due to overheating.

Air is completely removed from an electric bulb to prevent oxidation of tungsten filament.

When an electric bulb breaks, there is a mild bang due to the air rushing in to fill the evacuated space.

A common fluorescent tube contains mercury vapour at low pressure.