How electricity has changed the world can be easily taken for granted. It permeates the whole world: it’s in our home, on the streets, in the gadgets we use, whole systems like transport and health care are completely dependent on it, and everything we do is connected to electricity. In fact, we don’t even have to look beyond our own body: we have electricity flowing inside us, too. Bioelectricity is electricity which is present in every living organism. Our reflexes and thoughts are made possible to the myriads of neurons communicating to each other via electrical synapses. One neuron, or brain cell, sends its signal to its neighbour via an electrical current. The transmission of this signal from neuron to neuron is the basis of our thinking process, it is the basis of our memory, it is the basis of us being conscious. Electricity, be it in a bulb or a brain, is what makes the world go round. But what is electricity?
To answer this, let us take an example most of us are familiar with: switching on the light. What is it that causes the bulb to light up when we flick the switch? When we turn on the switch, we are in effect closing a gap. That’s all flicking a switch does: to close a gap. But where is the gap, you ask. From the switch to the light bulb and back to the switch, there are wires, copper wires, connecting them. The connection is almost complete or closed except for a little gap at the switch. It’s like a bascule bridge. (A good example of which is the Tower Bridge in London, UK.) Unless the two platforms on either side are in contact with each other then nothing can cross the bridge. The two flaps on each side go up in the middle allowing river dwelling vessels to pass along the river. But by so doing, the cars on opposite banks of the river cannot cross the bridge.
A switch is no different. When it’s closed, it allows a certain type of traffic to flow. It allows tiny particles called electrons to flow round the circuit, round the path from the switch to the bulb and back again. The electrons, whose nature I’ve explained in previous blogs, are elementary particles that have this physical property called charge.
Charge is a fundamental property of matter just as mass is. Not all particles carry charge and some carry opposite charge to that of the electron. The electron has been assigned to have a negative charge. It definitely is charged but why it should be negative and not positive is not just a mere arbitrary assignment of this sign to the electron. A proton, for instance, has an opposite charge to that of the electron; we therefore say that it is a positively charged particle. A neutron, which is another constituent of the atom, has no charge at all. It lacks this property shared by its positive and negative neighbours in the atom. It is neutral: neither positive nor negative.
So, the electrons are the ones going round and round the circuit from switch to bulb and back. Their movement round this circuit, them whizzing past through the wires, is what we call electricity. Their trip round this circuit, however, is not a smooth ride. They encounter a lot of traffic. Just like when you are in a rush and is trying to make your way through a crowd, the electrons in the wire encounter other electrons and atoms in their path. They have to struggle to go through and feel a lot of resistance as a result. This resistance is even more pronounced in the filament of the bulb than along the wires. In fact, the resistance is so high that it is as though they have to fight their way through the crowd of atoms in order to be able to keep circulating. To use the analogy of the crowd, it would be as though you have this mob in front of you trying to stop you from going past them and you are trying to fight back and make your way through. In this hustle things get quite heated up eventually. You feel hot and break into a sweat. Similarly, in the filament of the bulb, things get heated up as electrons try and make their way through the crowd of atoms. But the filament doesn’t just break into a sweat. It gets white-hot, literally. It gets so hot it starts to emit light. And the light emitted by the hot filament in the bulb is due, in the first place, to you closing the gap and allowing the traffic of electrons to flow. What’s even more amazing is that all of this happens in an instant. Unlike you taking minutes to make your way through the mob and down the street, the electrons go round the circuit, bump against the atoms in the filament, cause them to heat up so much so that the filament starts to radiate and lights up the room, all in a tiny fraction of a second! The simple action of switching on the light isn’t so mundane after all once you realise how much is going on and how fast as well.
This is the beauty of Physics: there are so many amazing things happening around us, and in us, all due to the mechanism and laws of Physics. And it is easy to take them for granted or to assume that they must be complicated and beyond comprehension. We don’t have to memorise the relationship between current and resistance or voltage to appreciate that electricity and switching on a circuit is down to electrons moving in the wire and causing a bit of a stir in the filament.