It is a well known fact that liquids in a horizontal tube would not flow, current would not be able to flow through the wire of copper on its own. Just in case, the edge of one tube is linked to a water tank in such a manner that there happens to be a difference in pressure between both the edges of the horizontal tube, there happens to be the pour out of water from the end at the other side at a rate that is stable. The water rate that flows out relies on the difference in pressure, for the pipe provided. If the current (flow rate) is expected to be stable always, water that flows away, for example, would have to be reversed into the vessel to contain the head of pressure. This urges the matter to be handled by an outside entity.
The analogy mentioned above showcases various features of the flow of electric current moves across. The electric current manages to flow through a conductor in cases only where there happens to be an potential difference of electricity between its both edges. To keep a current flow that is stable, one needs assistance from an entity, which manages to take care of the flow of charge. This entity is known by the name Electromotive Force or emf.
How to define Electromotive Force:
Current at all times flows in a circuit that is closed and secure. When a circuit that is closed (made with wire of copper) would be linked with the source of the electromotive force, latter would guide the charge of electricity to travel in a single stream which would comprise the current. The generators batteries could be the right source for electric charges.
Emf could be somewhat similar to the pump for charge. Whenever the source of emf is linked between both the conductor edges, it would guide the charges to travel from the lower potential region to the higher potential region.
Electromotive force could be stated as the work done per unit of charge. SI unit of Electromotive force is Volt.
For example, in the image provided underneath a resistor is linked to the energy source which here is the battery. Let us assume that the wires that are linking the battery and resistor are not creating any blocks to the current flow. The battery would have two terminus’s – Positive and negative terminal. The terminal with the positive charge would be having a higher potential energy when compared to the negative terminal.
Here if we disregard the battery resistance internally, there would be a difference in potential through the battery.The battery’s terminal voltage would be at par to the electromotive force of it . However in real-world situations mostly the battery would have some internal resistance , every time there is a current moving through the circuit.
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