How Does Electricity Work?

Written: Aadarsh Srinivasan

Imagine you have a circuit with a battery, a switch, and a lightbulb. It is intuitive that when you close the circuit, the lightbulb turns on, but what is not as obvious is how it happens. On the surface level, it is because the electrons are passing through the lightbulb, giving it electricity, and powering it on. But, that’s not the full story. This article from Science ReWired will explore electricity and how this amazing phenomenon came to exist.

First, we must go back to the late 1800’s when John Maxwell discovered that light comprises 2 oscillating fields that act perpendicular to each other as waves. These are the electric and magnetic fields, hence why light is considered electromagnetic.

The propagation direction of the light is perpendicular to both fields. John Poynting, a student of Maxwell, came up with an equation to determine the amount of electromagnetic energy passing through an area per second. This equation is known as the Poynting vector.

E x B is the cross product of the electric field and magnetic field vectors. µ0 is a quantity that measures the impact of free space on the two fields.

However, it was later realized that Poynting’s Vectors can actually work for anything with oscillating electric and magnetic fields, as long as they are in phase with each other; electricity, luckily, falls under this category.

Let’s take a simple circuit with a battery, a switch, and a lightbulb. When disconnected from everything, the battery has an electric field, but no magnetic field, since there are no moving electrons. When it is in the circuit, and the switch is turned on, the electric field is extended around the circuit, which causes the electrons to start moving. The electrons pass through the wire making the conductive material negatively charged while the electrons travel to the bulb, and positively charged while they return to the battery. The circuit now has 2 poles, so it creates a magnetic field around the circuit. Since there are now electric fields and magnetic fields present around the wire, the Poynting vector can be utilized to determine the direction and magnitude of the electromagnetic fields.

Using the right hand rule, you can put your fingers in the direction of the first field, and curl your fingers in the direction of the second field, and your thumb will be pointing in the direction of the flow of energy.