Problem 3.359

In the inertial reference frame \(K\) there is a uniform magnetic field with induction \(B\). Find the electric field strength in the frame \(K^{\prime}\) which moves relative to the frame \(K\) with a non-relativistic velocity \(\mathrm{v},\) with \(\mathrm{v} \perp \mathrm{B}\). To solve this problem, consider the forces acting on an imaginary charge in both reference frames at the moment when the velocity of the charge in the frame \(K^{\prime}\) is equal to zero.