Principle of the conductivity test:
Fondamental :
All the materials around us are made up of :
matter, which gives the material its shape
positive charges, which are bound to the material and are therefore fixed
negative charges: these are linked to matter to a greater or lesser extent, depending on the material. These are called electrons.
– If the material is conductive then current can flow in the circuit and the lamp can glow.
– If the material is insulating then the electric current cannot flow and the lamp does not shine.

For the bulb to light up, all of these elements must be conductors. We can thus determine whether a material is conductive or insulating.Electrical circuit diagram
Fondamental : Pouillet's law and electrical resistivity
Ohm's and Pouillet's law:

Fondamental : Local Ohm's law:

V and I are constant over time.
The resistivity ρ is an intrinsic parameter of the material.
Unit of ρ: Ω cm.