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` _{0}E_{0}`in` ^{'}_{r}cos(`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`R^{2}.
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 B_{0}