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Engineering Physics Study Material Unit-III Engineering Materials UNIT Ill - ENGINEERING MATERIALS DIELECTRIC MATERIALS Dielectric materials: The Dielectric materials are electrically insulators. The electrons are tightly bound to the nucleus of the atom and there are no free electrons. Ex: glass, mica, plastic, ebonite, rabber, wood, wax etc., © Dielectrics are non-metallic materials of high specific resistance and have negative temperature coefficient of resistance. If dielectric is used for insulation purpose then it is referred as insulating material but ifit is employed for charge storage then it is referred to as dielectric. @ All dielectrics are insulators but all insulators are not dielectrics. Definitions: 1. Electric dipole: Arrangement of two equal and opposite charges at a fixed distance is called electric dipole. @ @ = Ae 2. Electric dipole moment (1): The product of magnitude of any one of the charge of the electric dipole and the distance between two charges is called electric dipole moment. p=qxe It is vector quantity. SI unit is coulomb-meter or Debye, 1 Debye = 3.3x 10-30 C-m 3. Permittivity: It is the ability of a medium to allow electric lines of force to pass through it. It is the dielectric property of medium, which indicate the easily polarizable nature a material. Unit: Fm} or C2/N-m2 . Dielectric constant (Relative permittivity): It is defined as the ratio between permittivity of medium to the permittivity of free space. & K= € = oa : . It is dimensionless quantity and its value is 1 for vacuum. It is independent of size and shape of the dielectric. It is also defined as the ratio of capacitance of a capacitor with dielectric to the capacitance of same capacitor without dielectric. c K=€r= Co ; &. Electric polarization: When a dielectric material is placed inside an electric field dipoles are created in all the atoms inside the material. . - The process of producing electric dipoles which are oriented along the field direction is called polarization. 6. Dielectric Polarizability (a): The dipole moment induced in an atom is proportional to electric field E. Wek, y=0E, &= £ Where & is constant of proportionality known as polarizability. . . RHIT (Autonomous), Guntur ~ —_ . ‘ u www.Jntufastupdates.com Scanned with CamScanner 
