Chapter 6: Dielectrics and Capacitance

Quiz

1. Two dielectric regions have a planar interface at  (see figure). The field in region 1 is , V/m.

The relative permittivities of region 1 and region 2 are and , respectively. What are the field intensity and the polarization vector in region 2?

, V/m;
, C/m2
, V/m;
, C/m2
, V/m;
, C/m2
, V/m;
, C/m2


2. In a parallel-plate capacitor, the charge on the plates is  C. What is the electric flux density magnitude D, if the area of each plate is  m2. Assume uniform field distribution.

, C/m2

, C/m2

, C/m2

, C/m2



3. For the capacitor in Problem #2, find the voltage between its plates, provided its capacitance is C=10 pF.

, V

, V

, V

, V



4.The capacitor in Problems #2 and #3 uses dielectric of permittivity . The maximum allowable field intensity (dielectric strength) of this dielectric is  MV/m. (If , the material breaks down.) What is the maximum voltage , up to which the capacitor can operate safely (its breakdown voltage)?

, V

, V

, V

, V



5. A coaxial capacitor whose cross-section is shown in the figure below has a central conductor of radius  and an outer conductor of radius . The region between the two conductors consists of two regions: (i) the region  has a relative permittivity of  and (ii) the region  has a relative permittivity of . The radius  is such that  and  where .

What is the capacitance per unit length?