In this article I will try to explain the concept of electromotive force. We know that if we apply some potential difference between two ends of conductor electric current flows. But that’s not all as if we look closer we will find that it is not sufficient to apply just potential difference for maintaining current in the conductor. Thinking why I am saying so. Let me explain –
Let we have a conductor, in which charge carriers are electron. Suppose we have applied electric potential across to ends of the conductor. As soon as we apply potential difference electrons start to drift (and not start to move as they are already moving due thermal agitation.) towards positive terminal. As a result aggregation of electrons happens at higher potential terminal resulting in reduction of potential(due to set up of electric field in opposite direction on account of movement and aggregation of electrons). And soon applied potential is balanced by internal potential developed, resulting in stopping flow of current.
So we need some different mechanism which re-brings the charges in their original configuration i.e. stops aggregation of charges resulting in continuous flow of charge.
For that purpose we use special devices called Power Source, and one example of such a power source is battery. See the circuit :
Current is flowing as shown. Can you think what is the direction of current inside the battery. That’s good, it is in the same direction. If not so, our problem remains unsolved. Charge is again aggregated.
But now think on the situation in another way, look inside the battery ( reffer following figure).
See they are moving against they should. Is this Possible. I will like to compare the situation with this one ->
Suppose you have something in your hand. If you release it, you expect it to go down. But what if you release it and it goes up. Oh my God! you will be surprised.
But I will suggest you not see in this way. If you see marker flying up rather falling down, don’t think something impossible is happening. Just think from where this marker ( or stone or anything else what you released) is getting energy to overcome gravitational attraction. That’s all the case. There is some source of energy.
So, if current is flowing from negative plate to positive plate inside the battery don’t get surprised, just think how it is doing all this work? What is source of energy?
Let me tell now -> within battery some chemical reactions takes place which produce energy that results in this flow of current and this energy is electromotive force. Also note that as the name (electromotive force) indicates it is not a force.
that’s the end of the story.