Conductor

 Each solid-state material has its own characteristic energy-band structure. The electrical properties of solid-state materials depend on the variation in energy-band structure. According to their electrical properties, they are classified into conductors, semiconductors and insulators. In this section, the electrical properties of conductors, semiconductors and insulators are explained with their energy-band diagrams.

Conductor:

Every metal is a solid, which consists of a partly filled band structure. When an electric field is applied to the metal, the electrons are sufficiently energised and can move into higher states. These mobile electrons generate current and the metal behaves as an excellent conductor. The partly filled region is called the conduction band.

 (The substances which offer low resistance in the flow of electric current or the substances in which electric current can flow easily such substances are called conductors )

Classification of conductors:

 (1) With respect to physical appearance:

(b) Stranded conductor

(a) Solid conductor

(c) Multistranded conductor

(d) flexible conductor

 (2) With respect to properties:

(A) Flexible conductor

(B) Good conductor

(C) Bad conductor

(D) Non-conductor

Solid conductors: A single wire is known as single conductor. It is available in different diameter. It is used in cable and overhead lines .it is usually made on cuppor , aluminum steel etc....

Stranded conductors: The group of conductors of small diameter with respect to solid conductor is called stranded

conductor. In stranded conductor 1,17,19,37 strands having 1.13 to 3.37 mm diameter are used. It has flexible.

Multistranded conductors: These have smaller diameter with respect to stranded conductors. These are mostly used in multistranded wires and cables. These have 14, 22, 42 and 84 strands of each having 0.2 or 0.3 mm diameter.

Flexible conductors: These have smallest diameter. The numbers of conductors in flexible conductors are 14, 23, 40 and having dimeter of bless then 0.2 mm.

Properties of a good conductor:

The following are the properties of a good conductor:

(1) It should have high conductivity.

(2) It should have a low specific resistance.

(3) It should have a sufficient tensile strength. 

(4) It should be available at a reasonably low cost.

(5) It should have a high temperature coefficient.

(6) It should be easily joined and soldered.

(7) It should be available in large quantity

Name of the different types of conductor and their uses:

(1) Silver: It is a very good conductor and has a low specific resistance. But it is very costly so it is not used for general purposes. It is used in heavy duty contact points and sensitive meter.

(2) Copper: This is the most widely used material as a conductor, having the highest conductivity next to silver. It can be easily joint and soldered. It has high tensile strength so it is widely used in electrical industry for making the wires, cables, earthing electrodes etc.

(3) Aluminium: It has a conductivity of about 62% of that of copper. Now a days it is widely used due to less weight low cost, malleable and ductile. It is used for making wires and bus bars used in electric sub stations.

 (4) Brass: It is a harder alloy. It does not have any sparking effect on it, so widely used for making terminals electrical accessories like switch ,plug ,board etc

(5) G.I  wire : a wire having surface coated with a zinc to protect it from rusting,is called galvanised iron wire .it is used as a stay wire , earth wire .

(6) carbon : it is used for making brushes of electrical machine and filament .it has very high specific resistance

2. semiconductor:

                                Semi-conductors are those substances which are neither so conducting as conductors and nor they have so much resistance as insulators. They offer only some resistance in the flow of current, such as cloth, paper, water, coal, salt, silicon germanium etc.....

When the temperature is increase,some of the electron in the valence band get thermal energy, which is great then and move into the conduction band. These electrons are called free electrons and they can move whenever a small electric field is applied. Figure 10 shows the energy band structure of a semiconductor. The movement of electrons makes the substance slightly conducting and then the substance behaves as a semiconductor.

3. Insulator : insulator are very poor conductor of electricity.Insulators are those substances which will either not allow the current or allow very little current to pass through them. The resistance of an insulator is generally high.When an electric field is applied, the energy supplied by the applied electric field is too less to move the particle from the filled valence band into conduction band. As electrons are not sufficiently energised, conduction is impossible. Therefore, carbon and diamond act as insulators.

Properties of good insulator:

A good insulator should have the following properties:

(1) It should have a high resistance.

(2) It should have a high dielectric strength.

(3) It should be moisture and water proof.

(4) It should be easily moulded in any shape and size.

(5) It should have a large mechanical strength. 

(6) It should have a low cost and easily available.

The following are the insulators which are used in electrical works :

(1) Dry air: It is a good insulator. That is why it is possible to carry overhead distribution lines and transmission lines

parallel to each other and without any other insulation except at the point of support. It is also used in the condenser as an insulator between plates of the condensers. 

(2) Bakelite: It is a synthetic material which is made of different resins. It is water proof and can be moulded in any

shape and size. It is used for making of mould articles like sockets, switches, plugs, ceiling roses etc.

 (3) Porcelain: Porcelain has very good electrical and mechanical properties. It is made from china clay. It is used for making supports for distribution and transmission lines, bus bars in sub stations as a base for switch, kit-kat fuse, cleats for house wiring etc.

(4) Mica: It is a mineral product. It can easily split into extremely thin layer. It possesses high electric strength, high resistivity and can withstand high working temperature and is imprevious to moisture. Its draw back is that it has brittleness. It is used in electric iron, soldering iron, electric kettles etc.

(5) Vulcanised rubber: It is prepared by mixing the pure rubber, sulphur, zinc oxide with some colouring matters. It can be moulded into any shape. It dose not absorb moisture and it is also inflammable and has low conductivity It is used as a protective covering for low and medium voltage cable conductors.

Some important question and answer:

1.Ampere-second is the unit of

(a) power

(b) energy

(c) e.m.f.

(d) charge.                                              Ans=(D)

2.Force is measured in:

 (a) Newton/m

(b) Coulomb

(c) Newton

(d) Joule.                                               Ans=(c)

3.Which material is commonly used as conductor?

(a)glass

(b) copper

(c) ebonite

(d) rubber.                                            Ans= (B)

4.Whic of the following is a good electrical conducting material?

(a)brass

(b) copper

(c) zinc

(d) aluminum.                                     Ans= (B)

5.How many electrons are there in an aluminium atom?

(a) 13

(b) 18

(c) 29

(d) 43

                                                               Ans= (13)

6.What is the advantage of stranded conductors over solid conductors?

(a) More flexible

(b) More area of cross section

(c) More resistance

(d) More weight.                                    Ans= (A)

7.which material is not a good conductor

(A) porcelain

(B)steel

(C) copper

(D) aluminum.                                   Ans=(A)