Q.What is dielectric strength?

A dielectric (insulator) has no free charges, but an external field can still displace the bound charge within each atom or molecule, a process called polarisation. In non-polar molecules, whose positive and negative charge centres normally coincide (zero dipole moment with no field), an applied field pulls the two centres apart by a tiny amount, inducing a small aligned dipole moment in each molecule. In polar molecules (such as water), which already possess a permanent dipole moment even without any field but are normally oriented randomly by thermal motion (giving zero net polarisation on average), an applied field exerts a torque on each permanent dipole, partially aligning them and producing a net polarisation of the material as a whole. Either way, the resulting polarised dielectric -- now filled with a huge number of roughly aligned dipoles -- produces its own internal (induced) field that always opposes …