Electrostatic Fields in Matter

This leaves a layer of negative charge on the top surface of thedielectric and a positive layer at the bottom.The original charge Q, which was placed on the capacitor plates,is referred to as free charge.The charge induced on the dielectric surface is called bound charge.The bound charge generates a new field, in the opposite directionto the original field. This new field is called the depolarisation field.The total field in the dielectric is the sum of the original field (fromthe free charges) and the depolarisation field - it will be smaller thanthe original field.Bound chargesFree chargesDepolarisation fieldOriginal fieldLooking at equations (6) and (7), we see that when a dielectricis placed between charged plates which are not connected, then Qremains constant while V decreases; hence C increases. The factorby which C increases is called the dielectric constant K (or therelative permittivity, ɛ r ).-5