Dielectric

Fields in Material  Materials affect the electric field. Conductors block itConductors block it Insulators become polarizedInsulators become polarized  Polarized insulators decrease the field for the charge on the plates.    

Permittivity  Insulators have higher permittivity than the vacuum.  Relative permittivity is the ratio of the permittivity compared to the free permittivity of the vacuum.  Materials used for their permittivity are dielectrics. Relative permittivity = dielectric constantRelative permittivity = dielectric constant  Some dielectric constants (K): Vacuum Air Polyethylene 2.3 Paper 2-4 Mica 3-6 Glass 5-10 Body tissue 8 Ethanol 24 Water 80

Field Check  A point charge of 10 mC is surrounded by water with a dielectric constant of 80. Find the electric field at a distance of 20 cm.  The formula for a point source charge is  Using the values in the problem E = 28 kN/C. Factor of 80 times smaller than in vacuum

Capacitor Strength  A dielectric reduces the field for a give charge.  A dielectric also increases the charge for a given field.  The field is determined by the voltage and gap.  Dielectrics increase capacitance.    

Cell Regulation  Water has a very high dielectric constant: 80. Molecule naturally polarizedMolecule naturally polarized Fluid allows rearrangementFluid allows rearrangement  This allows very high charge storage across cell membranes

Capacitor Types  Shown below are capacitors Multilayer ceramic Ceramic disk Multilayer polyester Tubular ceramic Polystyrene Metalized polyester Aluminum electrolytic  Capacitors generally use dielectrics to increase the capacitance. next