Why is conductivity zero

If you understand electric circuits, then conductivity is analogous to the inverse of resistance. The electric field is similar to voltage, so voltage across a small resistor high conductivity will produce a large amount of current.

Voltage across a large resistor low conductivity will produce a smaller amount of electric current. Conductivity represents power loss within a material. Materials like air and vacuum space have no conductivity. When the conductivity is not zero, then an Electric Field flowing through the material will induce an Electric Current Density J.

Conductivity is a property of materials that determines conduction current density in response to an applied electric field. Recall that conduction current is the flow of charge in response to an electric field Section 6.

Although the associated force is straightforward to calculate e. The latter is determined by the mobility of charge , which is in turn determined by the atomic and molecular structure of the material. Conductivity relates current density to the applied field directly, without requiring one to grapple separately with the issues of applied force and charge mobility.

In the absence of material — that is, in a true, perfect vacuum — conductivity is zero because there is no charge available to form current, and therefore the current is zero no matter what electric field is applied. No currents are required for an EM wave to propagate; there are non in a vacuum I shall restrict this answer to only materials and their response to EM waves.

After all conductivity is a material property. Furthermore for this handwaving analysis I shall stick to materials who have linear response to the fields electric. The core argument still holds for non-linear responses but the analysis will differ. To begin, imagine the material to be consisting of electrons that behave as springs if perturbed from their equilibrium position linear response.

So the electrons have some inherent frequency with which they vibrate around the nucleus. These oscillations are damped due to inter-electronic repulsion and other things.

The external oscillating electric field then acts as a driving force to these electrons. This response of the electrons is what restricts the EM wave to propagate along the material. If the electrons did not interact with the field then the EM wave would propagate unhindered unrestricted to the material's geometry.

Thus there is inherent loss in the mechanism of conduction of EM waves in a material. In other words, conduction only occurs if there is a loss of energy that goes into oscillating the electrons that mediate the transfer. Superconductors have infinite, rather than zero, conductivity at DC, but they are lossless for DC current.

Ceramics, and polymers are usually good insulators, but you have to remember that polymers usually have a very low melting temperature. That means if you are designing something that will get very hot the polymer might melt, depending on its melting temperature. Electrical and thermal conductivity are closely related.

For the most part good electrical conductors are also good thermal conductors. Many products will contain both conductors and insulators- the conductors take the electricity or thermal energy where it is wanted and the insulators prevent it from getting where it isn't wanted. Silver has the highest electrical conductivity of all metals.