Educator

More on Filled Capacitors

• An electric field E exerts a torque on an electric dipole of diploe moment p. The torque is p*E*sin(theta), where theta is the angle between the E-field and the dipole moment vector. The torque tends to align the dipole with the field.
• The potential energy of an electric dipole placed in an electric field is

  U = –p.E = -p*E*cos(theta).

• When a parallel plate capacitor is filled with a dielectric (insulator) of dielectric constant K, the dielectric becomes polarized (a dipole moment is induced in the dielectric). This, in turn, causes a reduction in the value of E by K, and a corresponding increase in the value of the capacitance by K.
• Examples that show how to calculate the capacitance of a parallel plate capacitor if it is partially filled with a metal or a dielectric are given in the lecture.