What is the difference between voltage and current – quora static electricity bill nye full episode


When excess of charge is given to an insulated conductor, than due to mutual repulsion of charges, such an electric condition is created that those charges tend to fly away from conductor. A similar situation is created in the surrounding medium. Like charges of medium tend to fly away from conductor and unlike charges tend to move towards the conductor.If the surrounding medium is conductor, the charges will move out of conductor.Such an electric condition of any conductor is called electric potential.

A charged insulated conductor will have similarcondition on its surface and if joined to another uncharged conductor by aconducting wire electric charge from the one in which electric condition calledpotential is higher will flow to the other and thereby potential of first willdecrease and that of other will increase. The flow of charge will continue tillthe electric condition called potential is same on both the conductors. This isanalogous to the flow of liquid in a pipe due to pressure difference.

Electric potential being a physical quantity hence needs to be measured and have a proper mathematical expression. To measure the electric potential means to measure that electric condition which governs the flow of electric charges. We know that greater this electric condition on the surface of any conductor, greater will be the work done in adding a similar elementary charge (by bringing from infinity) on conductor’s surface. Thus we can conclude that:

EMF is (electromotive force) work done per unit +ve charge by internal mechanism of battery(source).this electrical work is done in a closed circuit to overcome the resistance of conductor joining +ve & -ve terminal + internal resistance of source(battery). Where as potential difference originate from electrostatic field created by charges accumulated on terminal of source. Electrical work done in case of PD only overcomes the resistance of conductor joining the +ve & -ve terminal of source. Because of this reason if nothing is connected externally than EMF=PD. though both EMF& PD being work done is voltage drop but concept of EMF does not hold much significance in open circuit. That’s why if you analyze Kirchhoff’s loop law,you can find that it mentions EMF and not PD.

If Ohm’s law can be written in the form V = IxR, and when R is zero then V is also zero even if there is a current. So answer to the statement that do current exist without voltage is theoretically yes. However I am afraid if practical existence of current without voltage is of only academic interest. We can have following examples:

1. Shorted DC source (a battery), I=V/R, at shorted condition R=0 Ohms, so we get I=V/0, then current would approach to a very large value (up to infinity), but that was mathematically (it assumes a zero internal resistance to the source), but in actuality internal resistance exists due to copper resistance from wires and connectors are additional to this, so voltage between two shorted point is also not exactly zero. One can say that current may exist even voltage is not present (for theoretical approach)