See Figure 1. To simplify, let the magnetic field point in the z -direction and vary with location x, and let the conductor translate in the positive x -direction with velocity v. Consequently, in the magnet frame where the conductor is moving, the Lorentz force points in the negative y -direction, perpendicular to both the velocity, and the B -field. The force on a charge, here due only to the B -field, is F y = − − q v B , while in the conductor frame where the magnet is moving, the force is also in the negative y -direction, and now due only to the E -field with a value: F y ′ = q E ′ = − − q γ γ v B .