If a person doesn't know what is dielectric or dielectric constant, then how ought one help him understand in laymans terms -what it is?? In bookish language it is "the ratio of the permittivity of a substance to the permittivity of free space". What this free space exactly? Please can anyone make me to understand this?
By free space people normally mean vacuum in which light travels at the speed of c. Refractive index, say n, the real part, and k, the imaginary part, is used to characterize the dielectric property of a material. The real part n reflects the speed of wave in the material, and k reflects the loss of energy carried by the wave.
For ideal dielectric materials, we expect a very low k value, resulting in very low loss. A n value over 3 is generally considered high.
We can understand what is dielectric constants in the sense that materials increase the capacitance of a capacitor(in relation to the air capacitance - Co). It is possible due dielectric constant of a material is larger than air or vacuum. For capacitors or resonators design both dielectric constant K and loss coefficient should be taken into account. For more information see the my article: Raman studies of polycrystalline CaCu3Ti4O12 under high-pressure.
If you'd like it in "simple terms", it may be easy to understand it through the current/voltage relationship. When an ac voltage (U) is applied to a material, it will induce current (I). This current consists of two components I=I1+I2: the ohmic component I1~U/R (movement of free charges, e.g. electrons) and I2~C(dU/dt) - the ac current induced in the polarized matter. Any matter with bound charges is polarizable, and vacuum behaves similarly (it is called "the dielectric displacement"). C is called capacitance and it is defined as the dieelctric constant multiplied by a geometric ratio (e.g. the area and the thickness of the capacitor). Thus, the higher the dielectric constant, the higher ac current will be inducced by an applied ac voltage.
Some examples:
In case of ac voltage is applied to almost nothing (free space or vacuum), the ac current will still appear I2>0. Tthis is how antennas work, they transmit signals even if almost nothing (only vacuum) is in between.
If the space is not free, but includes some bound charges, e.g. polarizable molecules, ionic crystal lattice, etc - all these will contribute to increase the dielectric constant and the related ac current (I2).
Finally, if the matter also includes free charge carriers (e.g. free electrons), they will contribute to the ohmic current (I1).
In summary, to get a high dielectric constant, one needs to get a substance with polarizable content.
In dielectric materials, which have no sufficient free charge carriers (such as free electrons), an ac voltage may still induce an appreciable ac current that will be directly proportional to the dielectric permittivity.
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