3. Consider a slab of current with non-uniform current density: j = Jo-k The slab is infinite in the y and z directions and extends from x = -d to x = d. (a) Argue conceptually (no calculation needed) that the magnetic field outside the slab (|z| 2 d) is zero. Hint: consider the slab as a set of parallel infinite sheets and use the principle of superposition. (b) Apply Ampere's law to find the magnetic field (magnitude and direction) at all points inside the slab. Hint: use an Amperian rectangle with its left side at x = -d and its right side at r. Remember that the field is zero at r = -d.