The principles behind solenoids are used extensively in Electro-mechanical systems to operate valves, control dampers, relays etc.

The solenoid may be used in both d.c. and A.C. circuits, the flow of electrons in both types of circuit create lines of magnetic flux which operate on the soft iron core Fig 5d illustrates the makeup of a solenoid for a water inlet valve,

All lines of Magnetic Flux become as short as possible in either AC or DC. If you place a soft iron or similar object within the field, the lines of force will distort and flow through the object