A large, thin conducting sheet located in the horizontal plane carries a uniform surface current per unit width \(K_0\). Directly above the sheet, the magnetic field is uniform with magnitude \(B_1 = \dfrac{\mu_0 K_0}{2}\) pointing parallel to the sheet. Directly below the sheet, the magnetic field has the same magnitude \(B_2 = \dfrac{\mu_0 K_0}{2}\) but points in the opposite horizontal direction. Which of the following best explains why the tangential component of the magnetic field undergoes a step discontinuity across the surface of the sheet?