Emt ch 5


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Emt ch 5

  1. 1. Ch 5Conductors, Dielectrics andCapacitance
  2. 2. Let us see what happens a number of electrons are placed on the interiorof a conductor . The electric fields set up by these electrons will repel each otherand accelerate away from each other. Finally these electrons will reach to thesurface of the conductor. The two characteristic of a good conductor are as under.1 No charge may remain within the conductor. As a final result zero charge density with in the conductor and a surface charge density resides on the exteriorsurface.2 For the static conditions, no current flows and this leads that the electricfield intensity within the conductor is zero. If it were not zero then it may apply aForce on the electron in valence band and may constitute a current.
  3. 3. 1 Two types of current carriers are present, electrons and holes.2 Holes are considered as positive charge carriers with μh.3 Electron with mobility of μe.4 Both the carrier move in the opposite direction in electric field but constitute the current in same direction.5 The conductivity is therefore a function of both hole and electron concentration and motilities.
  4. 4. P modify the E field in the magnitude and direction.The charge displacement in the form of dipole ,store energy that isuseful in the construction of capacitor.A conductor with finite conductivity will have a polarization.A dielectric in an electric field can be viewed as a free-spacearrangementof microscopic electric dipole composed of +ive and –ive charges whose center dont coincide.Dipole charges are not free charges and don’t contribute to theconduction process.Dipole are considered as a source of electrostatic field.All the dielectric materials store electric energy whether they are solid,liquid or gases and whether or not they are crystalline in nature.Polar molecules have a permanent displacement between the center ofgravity of +ive and _ive charges.
  5. 5. We first consider the tangentialcomponent of electric fieldusing the relation