Voltage and Current

Voltage and current are two concepts that can be daunting when we are initially trying to immerse ourselves in the world of electricity and electronics. After all, we all know that we shouldn’t put a fork inside an outlet if we don’t want to get shocked, or that for a light bulb to turn on it has to have a voltage between its terminals. But what exactly are these magical forces that make our facebook machines work?

To better understand these concepts, we need to go smaller: to the magic world of atoms; or, more specifically, of the little particles called electron.

Electrons are what we call a “Subatomic Particle”, which basically means that they are smaller than an atom; and they are, in fact, a fundamental part of it. Like all particles, we can assign them properties like a mass (9.1e−31 kg) and a charge (−1.6e−19 C); but we will come back to this later. For now, let’s just say that electrons are very friendly and spend most of their time bounding with other particles; and, much like childhood friendships, some of these bonds can be pretty tight and others looser.

The relationship between atoms, electrons and their neighbors vary between materials. We can imagine the atom as having several layers composed of electrons; and, if we look closely, we will see that the outer layer contains electrons that have not bound with any other atom yet: we call these “valence electrons” and they define how the elements interact with each other.

Some materials have more loose or free electrons than others: if a material is composed of electrons that are lazy and prefer not to move around much, it is called an “insulant”, such as wood or rubber. On the contrary, a material in which the electrons are adventurous and prefer to move and explore the world around them, we call call it a “conductor”, such as gold or copper.

But just being a “loose” electron is not enough to create electrical power. I mean, this is 2019 and we do not shame any electron for their behavior, but they do need something that gives them a little energy to go out and to their job. Now, if we put the electron on top of a hill instead of a flat surface, we can predict that it will start to roll downhill like a ball. This is what we call a potential, or a Voltage.

Physicists define Voltage as the difference of electrical potential between two arbitrary points. Basically, this means that the steeper we make this slope the more potential of falling the electrons will have. But on insulators, the bond between electrons and neighbor particles is strong enough to resist the increase in potential on the slope.

On the other side, not all materials are the same. Some of them can carry a bigger flow of electrons than the others. For example, the theoretic conductivity of silver (which is nothing else than the unit in which we measure how conductive a material is) is higher than that of, let’s say, gold for the same temperature; therefore, if we create slopes with these two materials, the slope made of silver will have a bigger amount of electrons flowing downhill.

The unit by which we measure this flux of electrons in a material due to a voltage slope is what we call “current”.

Now, the current that we obtain will depend on two things: the voltage and the conductivity of a material. For a higher voltage, we will create bigger currents of electrons, while smaller conductivities limit the amount of electrons that can flow which therefore causes smaller currents.

This relationship between voltage, current and conductivity is called Ohm’s Law and it defines the Current in function of the Voltage, the conductivity and the volume of a conductor. But this is something that we will develop more when we talk about resistors and resistivity in the future.

An interesting fact is that even though silver has a better conductivity than copper and gold, copper is most commonly used, given its cheaper price. Gold is also used for some applications that may need to be more resistant to corrosion.

Some other things come out of this relationship. For example, now that we know that the current depends on the conductivity of a material, we can modify its physical properties by, let’s say, inserting impurities into the conductor, making the flow of electrons more difficult. This is the process by which resistors and other electronic devices are created.

Another way to reduce the flux is to make the conductor so thin that it is actually hard for the flux of electrons to pass through. Moreover, the conductor is sometimes so thin that it heats up and emits light.

This is it for our take on Voltage and Current. However, we encourage you to come back and check our next articles on resistors and other electronic components!


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