As regards `in` 0 and `in` r (absolute and relative permittivity)
Assertion (A): In a perfect capacitor, the current density is given by `omega` `in` 0E0`in` 'rcos(`omega`t + `90^circ`), where `in` r' is real part of dielectric constant.
Reason (R): In a perfect capacitor, dielectric losses are zero.
If e is the charge of an electron, R is the radius of its orbit and `omega` is the angular velocity of electron, the magnetic dipole moment `mu_`m of the orbit is |`mu_`m| = e`omega`R2.
Assertion (A): In imperfect capacitors, the current does not lead the applied ac voltage by `90^circ` .
Reason (R): When subjected to ac fields, the dielectric constant can be expressed as `in` 'r - j`in` "r.
The core of a solenoid is made of material of relative permeability `mu_`r. A small cavity area dA and length dl is cut in the core. If it is desired that flux density in the cavity should be equal to B0