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.