A typical solenoid consists of the following main elements: a cyclindrical coil, a steel or iron frame or shell, a steel or iron plunger and optionally, a stationary magnetic pole/travel stop. A magnetic field is generated within the solenoid by passing electrical current through the coil. The frame or shell surround the coil, providing a flux path. In effect, it focuses the magnetic field produced by the coil. The plunger, being made of a highly magnetic material, reacts to the magnetic field by attempting to move to the centre of the coil. The plunger will travel to the centred position unless stopped by a load which exceeds the solenoids force capability, or the plunger contacts the stationary pole/travel stop. The force generated by a solenoid is dependent upon the current flowing through the coil windings.