What if I told you that I turned this lemon into a light switch. And what if I also told you that this lemon uses the same technology as the screen in your smartphone.

Before we can fully understand what is going on here let's Dive into the world of capacitors and capacitance. Capacitors are a type of passive component that are widely used In electrical circuits. They store small amounts of energy in an electrostatic field. Energy storage in an electric field is called capacitance. You can imagine them as a super small rechargeable battery that we stick into our circuit.
 

But how exactly do they work? Capacitor is created when two conductive surfaces come close to each other but do not touch. When we apply a voltage an electric field appears across the two conductors. And this is a form of energy storage. In between the two conductors there is an insulative material called a dielectric. This could be paper, ceramic, or even air.

These components are super simple, in fact we can even create our own using aluminum foil, paper, and some tape. First we need to cut out two squares of the aluminum foil. We then tape one of them onto one side of the paper, and the other on the other side of the paper. Next we connect a lead to each side so we can connect to it. Using our multimeter and measuring across the two leads we can see that there is a capacitance!

But you may be asking yourself why do we need these in our circuit. Let's look into a few examples of capacitors in circuits. The first reason is to provide a buffer of energy in our circuit. This is useful if we have components such as integrated circuits or other digital chips that need to sip power at will. If the battery is located at the opposite end of the circuit and it needs some power it is much better if there is a capacitor nearby to draw energy from.

The second reason is to filter analog signals. This is a circuit that provides a low pass filter, depending on the values of the resistor and capacitor you can change the frequency. Capacitors also play an integral role in a car radio, filtering out everything except the station you want to tune into. 

Lastly capacitors provide a large amount of current almost instantaneously. This is useful for photography flashes and strobe lights. And in fact if you were to open up a strobe light you would see that it mostly consists of capacitors! But be careful, since these can carry a high voltage that could hurt you.

Capacitors come in all shapes and sizes. After all we don’t have enough space in our electronic devices to cram our aluminum foil contraption into. So scientists have come up with different types of capacitor packages for use in different applications. The ceramic capacitor is the most widely used, as it is small. However, this capacitor is normally limited to small capacitance values. Next are film capacitors. These are normally used in environments where there is high temperatures or lots of vibrations. So you will normally find these in automotive applications. Lastly, we have electrolytic capacitors. These have a much larger capacitance than other types of capacitors and are constructed just like the one we made out of aluminum foil earlier. Except it is rolled up. These capacitors are normally used in power supply applications to smooth out the voltage in our circuit.

When we are dealing with electrolytic capacitors, one thing we need to pay close attention to is the polarity, which means it only goes in one way. If you were to put it in backwards, it could explode on you. And in fact, since it is known this happens they actually score the tops of capacitors to allow them to vent in a controlled manner. But they still will give you a good scare when they do blow. Capacitors also have a what is called a breakdown voltage, so when you are picking a capacitor to use in your circuit you want to make sure that it won’t be connected to a voltage source larger than that number.

One of the most widely used applications of measuring capacitance is the touchscreen in our phones. Our bodies have a certain capaticince, and when we touch our screen it is able to detect the capacity of our body through our finger. And this lemon is doing the exact same thing, when I touch it a capacitive touch sensor is being triggered causing the led to light up.