Ok this book is very common. It's the question number 6.5 A dielectric object that has a quasi-permanent polarization when the applied field is 0 is called an electret. Consider a uniformly polarized electret in the shape of a cylinder of height h and radius 10h. The polarization in the dielectric is P k^, where k^ is parallel to the cylinder axis. Note: It's a big P not small p. a. Sketch the electric field lines. b. Calculate the electric field E at the center of the cylinder. because the raidus is large compared to the height, you may neglect edge effects. c. Calculate the electric field E on the midplane of the cylinder, at distance 100h from the center. because the distance is large compared to the radius the dipole dominates the multipole expansion. At least give me a hint how to start. Thank you! And tell me how does electret different from other normal dielectric materials. ______________________________________________________ This is out of the book. A dielectric sphere is placed in an applied electric field. The radius of the sphere is a, and the dielectric constant is kappa (k). The electric field far from the sphere is Eo k^. Determine the dipole moment of the sphere, induced by the electric field. Thanks!