The armature, frame, and core of a 12-V DC control relay are made of sheet steel. The average length of the magnetic circuit is 12 cm when the relay is energized, and the average cross section of the magnetic circuit is 0.60 cm2. The coil is wound with 250 turns and carries 50 mA. Determine
a. The flux Density β in the magnetic circuit of the relay when the coil is energized.
b. The force F exerted on the armature to close it when the coil is energized.