Say, we have an alternating current source of max voltage V, and frequency v= 1 GHz connected to 2 plates as in a capacitor with an air gap of distance d, thus we get an oscillating electric field E, inside the capacitor plates, Emax = Vmax/d;, if atomised water is sprayed in between the capacitor plates the water molecules being permanent electric dipole experiences a force and torque in an non uniform oscillating electric field and thereby loses its energy in the form of heat to the surroundings. is this true?
Correct. The microwave oven works in a similar manner. Although the explanation is bit more precise when put in this way -
Since water molecules are polar in nature, they have a dipole moment; and they align themselves with the electric (electromagnetic, to be precise) field. If the field is oscillating, the molecules start rotating also. As the field reverses, the molecules also change direction. These molecules collide with each other, distributing energy throughout. This energy appears in the form of heat.
This is known as dipole rotation, and is used to raise the temperature of an object. This is the principle behind dielectric heating, which is used in microwave ovens.