My mornings in IIT Kanpur, where I teach, are interspersed with sips of green tea, the longing calls of peacocks and peahens, and the purposeless barking of my neighbour’s dog. Often making things interesting is a mess in the kitchen – the result of my tendency to ignore the milk I left on the stove, and remember it just as it boils, flows over the vessel, spills on the counter, and drools to the floor.
As I curse the milk, I also can’t help but feel some sympathy for the innocent victim of this mess: my stove-lighter. Resting there in innocence on the counter, it has no idea that it is having a bad day.
These lighters are magical pieces of equipment. A push with your thumb, something clicks, and there comes a flame. If you haven’t noticed it, go to your kitchen, pick up the lighter, point it towards yourself, and watch carefully. As you click it, you will notice a small spark flying between the central rod and the cylindrical covering. But don’t worry: unless you are flammable (regular human beings are not), there is no danger of you catching fire or even getting an electric shock.
This same spark accompanies the wonderful monsoons (which we eagerly await in Kanpur), just that they screech through the night sky and can add amazing percussions to a late night instrumental on the stereo.
What is it, then, that allows that small piece of equipment to create thunder in your kitchen, and at the innocuous push of your thumb?
To understand this, we first need to figure out what an electric spark is.
What is an electric spark?
A spark is essentially an electric charge flying in the air between two points, one of which has a large quantity of surplus electrons while the other has too few. This difference in quantities of electrons can happen due to many reasons. Sometimes people have engineered it this way using chemicals: the simplest example is the battery that we use in everything from remote-controls to electric vehicles.
A point with a large number of surplus electrons is called the negative terminal (since electrons are negatively charged) and a point that is deficient of electrons is the positive terminal. This is why you see ‘+’ and ‘-’ signs marked on every battery. In most situations – and unlike some people – electrons are extremely equitable in nature and dislike this difference in their quantities. So, given an opportunity, they will travel from a place where they are more in number to a place where they are fewer in number. This is why current flows when we attach a wire between the two ends of a battery, and in the process we make our fans move, or bulbs light up, etc.
However, if we don’t attach a wire and the electrons still want to move, what will they do?
Is lightning a giant spark?
If the gap between the surplus and the deficiency of electrons becomes too extreme, at some point, these electrons will lose all patience and decide to fly through the air, disrupting everything in between. This is not very dissimilar to human society. Sometimes, you might notice that something upsets people slowly over time, and then suddenly, there is a surprisingly large bit of unrest.
To be able to break out like this, electrons first need to break up air molecules mid-air, creating ions (charged atoms). In addition, many electrons inside the atoms are also pulled out, creating free electrons in the air. All this creates a region through which electrons can easily move – as if they have made a wire for themselves in thin air! And when they travel on this path, we see it as a spark.
Clouds are charged objects. When they move over large distances and collide with other clouds, they get more and more charged. At some point, this charge becomes too much for the clouds to hold, and breaks out as the lightning that we see (followed by the thunder that we hear).
How do our stove lighters, which are limited to our kitchens, create such powerful electronic unrest?
What is a piezoelectric material?
This has to do with a class of materials called piezoelectrics, which every stove lighter contains. Piezoelectrics are amazing materials with a particularly interesting property: they can effectively create a surplus and a deficiency of electrons when they are under some pressure. As it happens, they can also easily remove this surplus when the applied pressure is removed.
The reason these materials can do this is because the atoms in a piezoelectric material are arranged in a slightly funny periodic pattern. They also usually have two types of atoms that have two different charges. One has a surplus of electrons and the other has a deficiency, i.e. they are negative and positive ions.
Now, under no extra pressure, these atoms are arranged in an alternating pattern and in such a way that there is no surplus of electrons at one end compared to another. When some pressure is applied, the picture changes. The structure of these materials is such that, under pressure, the positive ions move in one direction and the negative ones move in the other direction. This creates a surplus at one end of the material and a deficiency at the other end. Essentially, the material has become a battery!
With some meticulous physics and engineering, this surplus/deficiency of electrons, created when the pressure is applied, can be made to be quite high – practically enabling the electrons to fly through the air, just like in the case of lightning. This is the spark you saw when you clicked the lighter.
Treat a lighter with respect
These flying electrons can ignite an inflammable object. So when the supply of cooking gas is on and you click the lighter near it, a fire erupts on your stove! Sometimes, the pressure applied is not enough to generate a spark, so at times you need to click it a couple of times, so that one of the hits is strong enough to create a sufficiently significant spark. (In case you are intrigued and interested in learning more about piezoelectric materials, taking a physics course on condensed matter physics may be worthwhile.)
So the next time you end up cooking something and it spills over your gas lighter – just like the milk I was boiling here at IIT Kanpur – please clean it with some respect. Every day, it creates tiny lightning bolts just for you, even if all you want to do is enjoy some crispy onion pakoras to go with the monsoon rain.
Adhip Agarwala is an assistant professor of physics at IIT Kanpur.
