I have a situation that a magnet is placed near to a coil. Especially in pumps and the pump is working based on the stroke mechanisam. The coil is powerd up by a DC source of 12volts and the piston(which having magnet on it) is attracted by this coil called as stroke. The distance between the coil and piston is 1Cm. Is that basic stroke is really coming from or due to coil? I am not uinderstood theoritically. If the coil is really attracts the piston, why then always stoke exist i.e. push and pulling back again. It has to attract by coil always. what is the cause for pushing back?