Basics of electricity | Charge, Voltage, Current

What is electricity?

In one sentence, a form of energy which is now an indivisible part of human life. Can you even imagine how life would be without electricity? It is all around us – lighting our ways, powering our gadgets, cooking our food, and many more things you can think of. But what exactly electricity is? And how does it work?

Electricity is a natural phenomenon that occurs throughout nature in many forms. Lightning stroke is the greatest example of natural electricity. An amber rod when rubbed on cat’s fur attracts light objects such as feathers. This is an example of static electricity and such examples were known to people long before the discovery of electricity. In Greek, ‘elektron’ is the word for ‘amber’.

Electricity can be briefly defined as the presence and flow of charge. But where does this charge come from? And why would it flow?

What is electric charge?

To understand electricity, we need to zoom into the atomic level. We know that an atom consists of three distinct particles – Protons, electrons and neutrons. Protons and neutrons reside in the nucleus while electrons orbit around it. Electrons in the outermost orbit are called valence electrons. With enough external force, valence electrons can escape the orbit and become free to move.

copper atom, positive and negative charge

Charge is a property of a matter, just like mass, volume etc. And it is measurable. There are two types of charges – positive and negative. Protons carry positive charge while electrons carry negative charge. Neutrons, true to their name, are neutral and do not carry any charge. In the stable state of an atom, the number of protons and electrons is equal. And therefore, net charge of a stable atom is neutral. If there are excess electrons, it will be negatively charged. And if there is a deficiency of electrons, it will be positively charged. There is a force of attraction between similar charges while opposite charges repel each other. This force is known as electrostatic force.

What is electric voltage?

Basically, the difference in charge between two points is known as voltage. Let’s take an example of wax and wool which have been rubbed together. We find that there is a force of attraction between wax and wool after rubbing. This is because there is a surplus of electrons in the wax (negative charge) and a deficit of electrons (positive charge) in the wool due to rubbing. With no path for electrons to flow from wax to wool, all we can see is the two objects attracting together due to the electrostatic force. But, if a conductor is placed between them, electrons will flow through it (we will see this under the next heading).

The difference in charge between two points can be created by means other than rubbing certain types of materials against each other. Some popular ways include chemical reactions and influence of magnetism. You must have seen many batteries in everyday life. You know there are two terminals, one is marked positive (+) and the other is negative (-). Because of the chemical reactions in a battery, there are excess of negative charges (excess electrons) on the negative terminal. Whereas, there is a deficiency of electrons on the positive terminal. So, there is a difference in charge between the two terminals of a battery.  This is the voltage or potential difference between the two terminals which is waiting to act.

battery charge distribution

We see excess of negative charges at the negative terminal and positive charges (deficiency of electrons) at the positive terminal of a battery as shown in the above picture. The atoms or molecules of the material in a battery will seek to be neutralized. Therefore, the negative terminal will tend to push away electrons while the positive terminal will tend to attract electrons. Such tendency is known as voltage or potential difference. But, the negative terminal cannot simply push away electrons in the air or the positive terminal cannot simply gain electrons from it. Air is an insulator, which means valence electrons of air molecules are difficult to be freed.

What is electric current?

Suppose a conductive wire is connected between the positive and negative terminals of a battery. (Valence electrons in conductive materials are easy to move). So the negative terminal of the battery can now push away electrons into the conductor. Simultaneously, the positive terminal will pull electrons from the conductor. Electrons will move from atom to atom within the conductor as shown in the animation below.

electron flow within a conductor
Image Credit: sparkfun

As shown in the animation above, same electrons from a battery do not actually travel the complete path. Instead, the charge flows along the path. This flow of charge is known as electric current. However, a current can only flow through a continuous loop or closed circuit. Electrons (and, hence, current) will not flow if the path or conductor is broken at any point.

battery electron flow animation current

However, connecting a pure conductor directly across a voltage source is a bad idea. In such case, energy moves very quickly and is transformed to heat in the conductor which may consequently result in melting of the conductor and fire hazard.

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