The Relay
How can an electric circuit, - namely a 'logical' controlled one - be made to keep its state?
Let us pursue this question by a rather solid example: the earlier mentioned electrically actuated electric switch, the relay:
Its principle is rather simple: An electro-magnet (that is a spool of insulated copper wire around a iron core) becomes magnetic, when a current is flowing between the points E1 and E2. Now the "contact tongue" is pulled down and the current - formerly passing between A and B will now be led between A and C. When the current is off, the core will immediately loose its magnetism, and the contact tongue will switch to its former position AB.
Indeed we have now two separate circuits, what is of no importance for us - as it is the possibility af actuating more than one switch at a time.
move on