The force carried by the plunger of the door chime of given figure is determined by
Where dφ/dx is the rate of change of flux linking the coil as the core is drawn into the coil. The greatest rate of change of flux will occur when the core is ¼ to 3⁄4 the way through. In this region, if changes from 0.5 x 10-4 Wb to 8 x 10-4Wb, what is the force carried by the plunger?
