We use terms such as current, voltage, as part of our daily routine. What are they? Let us see their meanings and relationship with each other.
We have seen what is static electricity. In this article, we talk about current electricity.
Current
Electrons in an atom can be separated from their atoms. Valence electrons are the outermost electrons that can be made loose. It is possible to make these electrons move in a particular direction. The movement of electrons is called current. The working of the gadgets mentioned is due to the electric current flowing through them.
Current is defined as the rate of flow of charges through a wire. Charges (electrons) move through a wire. The amount of these charges moving through a wire at a particular time is defined as current.
I = Charge (Q)/time (t)
where ‘Q’ is the number of charges. Its unit is Coulombs (C)
‘t’ is the time in seconds (s)
‘I’ is current. Its unit is Ampere (A), after the French scientist, Andre-Marie Ampere who did a lot of work on current electricity.
For the current to flow, the circuit must be closed. It means that the wire and all the components used must be in the form of a loop.
The amount of current in a wire is measured using an instrument called an Ammeter.
Potential Difference
Now that we have seen what is current, let us know what makes the charges move inside a circuit. It is due to a quantity called potential difference.
There is an electric field around a charge. We know that like charges repel each other. So, to move a positive charge towards a field created by another positive charge, work must be done against this repelling force. This work done to move a charge from infinity (a region outside the field) to a point inside the field is called the potential at that point.
V = Work (W)/Charge (Q)
When work (W) is done in moving a charge (Q) from one point to another in a field, it is called Potential Difference (V) , between those two points.
Let us understand this with an example that we can relate to:
To lift an object that is on the ground to a height, A, against the gravitational force, we need to do work. The energy at that height is called potential energy. If we move this object from A to another height B, then there is a difference in potential energy from A to B.
Electric potential difference is somewhat similar to the example given. If there is a movement from higher potential to lower, there is a fall in potential, else, there is a rise in potential.
The SI unit for potential difference is Volt. The potential difference between two points is when work of 1 Joule is done in moving 1 Coulomb of charge between these two points. In common terms, it is also called voltage. The higher the voltage, the higher is the force to move the charges in the circuit.
Electromotive force (emf)
We have seen battery cells with 1.5 V, 3 V, 6 V, 24 V written on them. The potential difference between two terminals of a battery cell when there is no circuit connection is called the electromotive force (emf) of the cell. That is, it is the voltage of the battery when no current is flowing out of it.
Relation between voltage and current
Voltage or potential difference makes current flow. For current to flow in a circuit, there must be a potential difference. We can understand it easily by using an example.
Suppose there are two tanks filled with water and connected by a pipe. If the level of water is the same in both, there is no movement of water between them.
If the height difference is zero, water movement is zero.
Similarly, if the potential difference is zero, charge movement (current) is zero.
Similarly, the difference in potential between two points causes the current to flow from the point of higher potential to that of lower potential.
Just as in the water analogy, the difference in height or pressure causes water to move, the potential difference causes charges to move, creating a current.
a. Flow of water
b. The difference in height
c. The height difference is zero
d. Motor pump
a. Flow of current
b. Potential difference (voltage)
c. No current flow
d. Battery cell
There is a relationship between electric current and voltage, given by one of the fundamental laws of electrical engineering, called the Ohm’s Law. We will know about that in another article.
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