Griffiths electrodynamic problem 5.17solution page 240

A large parallel-plate capacitor with uniform surface charge σ on the upper plate and −σ on the lower is moving with a constant speed v,asshownin Fig. 5.43. (a) Find the magnetic field between the plates and also above and below them. (b) Find the magnetic force per unit area on the upper plate, including its direction. (c) At what speed v would the magnetic force balance the electrical force?