Theory of the Hamaker constant

Examination of Table 7.2 reveals some interesting features, such as the effect of the medium in between two macroscopic bodies, which clearly 

This is a fundamental property of dielectrics and means that if the charge on the plates is fixed, the potential difference between the plates and hence the electric field inside (in the dielectric) must have fallen 

Molecular dipoles produce local field in opposite direction 

Now let us examine what would happen to the response of the dielectric if we put an alternating voltage on the capacitor of frequency co. If CO is low (a few Hz) we would expect the material to respond in a similar manner to the fixed-voltage case, that is d (static) = e(co) = e(0). (It should be noted that eo, the permittivity of free space, is not frequency-dependent and that E(0)/eo = H, the static dielectric constant of the medium.) However, if we were to increase co to above microwave frequencies, the rotational dipole response of the medium would disappear and hence e(co) must fall. Similarly, as we increase co to above IR frequencies, the vibrational response to the field will be lost and e(co) will again fall. Once we are above far-UV frequencies, all dielectrics behave much like a plasma and eventually, at very high values, e(co)lto = 1. 

What is actually happening at the frequencies co, where there is a sudden reduction in the response of the dielectric We can, in fact, treat 

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