Consider the device like a primitive relay. The armature on the right would be guided and aligned with the core on the left. A return spring would be used to pull the armature back to the right once the coil is de-energized. The springs effect is addressed below. As a relay some contacts are connected to, and move with, the armature. Other contacts are stationary and would make or break contacts as the armature moves. The following characteristic re given: Core and armature material = cast steel, us Fig 1-5(b), pg. 3. N = 500 turns Mean core path through the core and armature = 360mm Each air gap between core and armature = 1.5mm With the given airgap, a flux density B = 0.8T is required to move the armature and actuate the relay. This is required to overcome the spring. Determine: (a) Find the current in the coil. Hint: the air gap is so small, fringing is negligible. (b) What is the permeability of the relay's magnetic circuit, m, assuming (a). (c) Repeat the problem with the air gaps zero. Find the new current necessary to maintain B = 0.8T.