Q4. (5 marks) A variable reluctance sensor consists of a core, a variable air gap and an armature. The core is a steel rod of diameter 20 mm and relative permeability 200. A coil of 300 turns is wound onto the core. The armature is a steel plate of length 10cm and thickness 0.5 cm and relative permeability 500. Assuming the relative permeability of air = 1.0 and the permeability of free space = 4xx10-7 Hm -1, calculate the inductance of the sensor for air gaps of 10 mm. Target, Displacement gap Scm Coil To output unit