Problem 3.370

In an inertial reference frame \(K\) there are two uniform mutually perpendicular fields: an electric field of strength \(E=40 \mathrm{kV} / \mathrm{m}\) and a magnetic field induction \(B=0.20 \mathrm{mT}\). Find the electric strength \(E^{\prime}\) (or the magnetic induction \(B^{\prime}\) ) in the reference frame \(K^{\prime}\) where only one field, electric or magnetic, is observed.

Instruction. Make use of the field invariants cited in the foregoing problem.