Energy of a dielectric rod Let a dielectric rod kept in an electric field (initially in equilibrium) be rotated by an angle, and then released. Is some energy stored in it (the rod)? Why? What is the value of this energy? How can I come up with energy for dielectric of arbitrary shape? 
 A: A dielectric consisting of polar molecules initially in random orientations when no electric field is applied will undergo some degree of polarization by orienting the dipole moments of the polar molecules to align them with an external electric field. 
If either the rod of such a dielectric is rotated in a stationary field, or the field is rotated with the dielectric stationary, the dipoles will reorient themselves accordingly. This reorientation result in heating, sometimes referred to as dielectric heating. This is the basic principle of dielectric heating of a such a material if it is exposed to an alternating electromagnetic field, such as the electromagnetic field of a microwave oven used for cooking, or medical diathermy equipment use to heat tissue for therapeutic purposes.
Insofar as quantifying the energy losses associated with dielectric heating, you can start by Googling the subject. The Wikipedia article on "Dielectric Heating" gives one equation (though marked "citation needed").
Hope this helps. 
