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Electrical Engineering Materials

by Ajit Sahu
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Ajit Sahu
Ajit Sahu
CONTENT GENERATION UNDER EDUSAT PROGRAMME Electrical Engineering Material (EET-302) Contributors:1. Sri D.C. Behera, Sr. Lect. (Elect), B. O. S. E. Cuttack 2. Sri P.R. Tripathy, Asst. Prof., K.P. Bhubaneswar 3. Sri A.K. Sahu, Lect. (Elect) G.P. Gajapati
INDEX Sl No. 1 2 3 4 5 6 Contents Conducting materials Semi-conducting materials Insulating materials Dielectric materials Magnetic materials Special purpose materials
Conducting Materials 1. Introduction An electrical engineer should posses the knowledge of the properties of materials used in electrical engineering. This knowledge helps to choose the correct materials for a given application. Hence, the materials available can be employed effectively and economically for a specific purpose. 2. Classification of Electrical Materials  Materials used in the electrical engineering field are classified basing on their properties and applications. a. Conductor materials. b. Resistor materials. c. Insulating materials. d. Semiconductor materials e. Magnetic materials f. Refractory materials g. Structural materials.  Classification of Materials Based on Atomic Structure The materials such as gold, silver, copper and aluminium which can neither be broken into other substances nor be created are called „elements‟. The smallest particles into which an element can be divided having the identity of the element are called „atoms‟. These particles cannot be divided further. The atom although extremely small, has a complex internal structure of its own. This resembles the miniature solar system. An atom consists of the central core called nucleus, with electrons revolving around it as well as spinning around themselves. The nucleus contains protons and neutrons. Each proton possesses as much positive charge as an electron possesses negative charge (1.6 x 10-19 C). The number of protons inside the nucleus is equal to the number of electrons revolving around it. This number is called atomic number of the element. The neutron does not possess any charge. Therefore, the atom is electrically neutral. The mass of a
proton or a neutron is 1.672 x 10-27 kg. which is 1850 times more than that of an electron. The mass of an electron is 9.107 x 10-31 kg. The electron‟s diameter is three times that of a proton. The weight of protons and neutrons together is called atomic weight of the element. The electrons are held in the atom by attractive force between protons and electrons which carry opposite charges. The electrons revolve in successive orbits or shells. The orbits should be visualized to be in different planes and not as they appear to be in the figure. The number of electrons that each shell can accommodate is given by 2n2, where n is the number of the shells counting from the innermost shell. The innermost shell (i.e. the first shell) can accommodate 2 electrons, the second shell 8, the third 18 and so on. The outermost shell in no case will contain more than 8 electrons in the first shell, 8 in the second, 8 in the third and 1 in the fourth even though the third shell can accommodate 18 electrons according to the formula. Within the shell there are sub-shells which are classified as : s, p, d, f, g, s and p and so on. There are energy levels Fig 2.1 again in these sub – shells. The sub-shell s has one energy level, p has three levels, d has five levels and so on. Not more than two electrons occupy the same energy level, one spinning in one direction and the other in the opposite direction. Thus the sub-shell S can accommodate 1 x 2 = 2 electrons P can accommodate 3 x 2 = 6 electrons D can accommodate 5 x 2 = 10 electrons F can accommodate 7 x 2 = 14 electrons G can accommodate 9 x 2 = 18 electrons and so on. Shell Possible sub-shells 1 or K 1s 2 or L 2s 2p 3 or M 3s 3p 3d 4 or N --------- 5 or O --------- 6 or P 6s 6p 6d 6f 6g 6h

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