Dielectrics Experiment Place dielectrics between plates of capacitor

Dielectrics Experiment: Place dielectrics between plates of capacitor at Q=const condition Observation: potential difference decreases to smaller value with dielectric material relative to air Without dielectric: because V<V 0 C>C 0 With dielectric: K>1: relative dielectric constant

What happens with the E-field in the presence of dielectric material We know V<V 0 E<E 0 specifically d reduced with dielectric material The surface charge (density) σ on conducting plates does not change but induced charge σi of opposite sign and Definition of the permittivity

DIELECTRICS +Q Example: E 0 E 1 E 2 K 1 K 2 d/2 -Q V

24. 4 DIELECTRICS Dielectric breakdown or Dielectric strength High Voltage Ground Air Cr 2 O 3

GAUSS’S LAW IN DIELECTRICS Conductor Dielectrics A A A

GAUSS’S LAW IN DIELECTRICS Example: Capacitance of half filled spherical capacitor K E 1 ra r rb E 2 Check: K->1 needs to reproduce empty

MOLECULAR MODEL OF INDUCED CHARGE E E

CLICKER QUESTION A conductor is an extreme case of a dielectric, since if an electric field is applied to a conductor, charges are free to move within the conductor to set up “induced charges”. What is the dielectric constant of a perfect conductor? A. K = 0 B. K = C. A value depends on the material of the conductor 8