The force to close a relay electromagnetically can be found

The force to close a relay electromagnetically can be found by :

-integrating the current as it open for a small gap.

- matching the mechincal energy and stored magnteic energy for small change.

- computing the change of energy in the iron .

- examining the change of energy in the iron for a change in gap.

Solution

Ans: Matching the mechanical energy and stored magnetic energy for small change