A block of a solid is known to contain many dipoles aligned in the same direction (such a material is known as an electret).

A block of a solid is known to contain many dipoles aligned in the same direction (such a material is known as an electret). In an electric field of magnitude , the block tends to orient itself so that the dipoles are aligned along the electric field lines. If are required to rotate the solid so that the dipole directions are reversed, and each dipole has dipole moment how many dipoles are there in the block?