One of the questions that's often asked by new students, is why don't we switch it around so the current points this way? Why don't we assign an electron, why don't we make current go this way?
So, why didn't we just switch it around? Well, we had a years of experience, and now we've actually had another , since the discovery of the electron. And we've managed to get by with this. We have not chosen to do it. One of the reasons we don't do it is because it would basically, it would be a big mess. Imagine if for instance, say in the United States we decided, Oh, driving on the right side of the street is the wrong side of the street. We want to all drive on the left. Imagine the chaos that would cause.
Now, before we made the change, everybody managed to get where we were going, and after the change, everybody would get there going, but the change over would be just so, so costly.
And the same thing with electricity. We can do perfectly well talking about current going the direction of a positive charge, just like we did here with the positive sodium going in this direction. This is actually how electricity is conducted in your body.
So, it's not uncommon to have positive charge moving around. That's the definition of current in a nutshell. This vacancy or hole has a positive charge. If an electron passes near the hole, it will be attracted and it will fill the hole, completing the co-valent bond.
Current flow in this type of semiconductor material is by way of holes. This type of semiconductor material is referred to as P-type material. P means positive, which refers to the charge of the hole. When an electrical voltage is applied to a piece of P-type semiconductor material, electrons flow into the material from the negative terminal of the voltage source and fill the holes. The positive charge of the external voltage source pulls electrons from the external orbits, creating new holes.
Thus, electrons move from hole-to-hole. Electrons still flow from negative-to-positive, but holes move from positive-to-negative as they are created by the external charge.
In certain types of materials, particularly liquids and plasmas, current flow is a combination of both electrons and ions. Figure 8 shows the simplified drawing of a voltage cell. All cells consist of two electrodes of different materials immersed in a chemical called an electrolyte. The chemical reaction that takes place separates the charges that are created. Electrons pile up on one electrode as it gives up positive ions creating the negative terminal while electrons are pulled from the other electrode creating the positive terminal.
Whenever you connect an external load to this battery, electrons flow from the negative plate, through the load, to the positive electrode. Inside the cell, electrons actually flow from positive-to-negative while positive ions move from negative-to-positive.
So why do we continue to perpetuate the myth of conventional current flow CCF when we have known for a century that current in most electrical and electronic circuits is electron flow EF?
I have been asking that question of my colleagues and others in industry and academic for years. Despite the fact that electron flow is the reality, all engineering schools insist on teaching CCF.
If you were in the armed services or came up through the ranks as a technician, chances are you learned and favor electron flow. The way you learned it in school is what you tend to use when you design, analyze, troubleshoot, or teach out in the real world. As you may know, it doesn't really matter which current direction you use as circuit analysis and design works either way.
In fact, this issue only affects DC that flows in only one direction. In alternating current, electrons flow in both directions, moving back and forth at the frequency of operation. But if it truly does not matter which direction we assume, then why don't we default to the truth and end this nonsense once and for all? If you ever want to start a lively conversation, maybe even an argument, try bringing up this subject in a group of technical people.
You just may be surprised at the intensity of the feelings and the sanctimonious attitudes on both sides. I've done this numerous times and I am still amazed at the emotional response this issue generates. My conclusion is that the concept of CCF will never be abandoned. It is somewhat akin to forcing us all to switch to the metric system of measurement using meters and Celsius rather than feet and Fahrenheit with which we are more familiar and comfortable.
CCF will continue to be taught from now on. I have come to accept this whole thing as one of the stranger quirks of electronics. Early researchers of electricity first discovered the concept of voltage and polarity, then later went on to define current as the motion of charges. The term voltage means the energy that makes current flow. Initially, voltages were created by static means such as friction or by lightening. Later, chemical cells and batteries were used to create a constant charge or voltage.
Mechanical generators were developed next. Charges refer to some kind of physical object that moves when it is subjected to the force of the voltage. Of course, back in the 18th century, those working on electrical projects didn't really know what the charges were. For all they knew, the charges could have been micro miniature purple cubes inside a wire or other conductor. What they did know was that the voltage caused the charges to move. For purpose of analysis and discussion, they arbitrarily assumed that the charges were positive and flowed from positive-to-negative.
This is a key point. They didn't really know the direction of current flow, so they theorized what was happening. And, as it turned out, they guessed wrong. There is nothing wrong with being wrong as scientists are often hypothesizing one thing, then later finding that the truth is something else.
An electric current is viewed as flow of positive charges from the positive terminal to the negative terminal. This choice of direction is purely conventional. As on today, we know that electrons are negatively charged and thus, the conventional current flows in the direction opposite to the direction of electron motion. Also, since electrons move from lower potential to higher potential in an electric field, the current thus flows the opposite and it is easier to visualize current flowing from a higher potential to a lower potential.
Why does a current flow from positive to negative? Thus, these negatively charged electrons move in the direction opposite the electric field.
But while electrons are the charge carriers in metal wires, the charge carriers in other circuits can be positive charges, negative charges or both. In fact, the charge carriers in semiconductors, street lamps and fluorescent lamps are simultaneously both positive and negative charges traveling in opposite directions. Ben Franklin, who conducted extensive scientific studies in both static and current electricity, envisioned positive charges as the carriers of charge.
As such, an early convention for the direction of an electric current was established to be in the direction that positive charges would move. The convention has stuck and is still used today. The direction of an electric current is by convention the direction in which a positive charge would move. Thus, the current in the external circuit is directed away from the positive terminal and toward the negative terminal of the battery.
Electrons would actually move through the wires in the opposite direction. Knowing that the actual charge carriers in wires are negatively charged electrons may make this convention seem a bit odd and outdated.
Nonetheless, it is the convention that is used worldwide and one that a student of physics can easily become accustomed to. Current has to do with the number of coulombs of charge that pass a point in the circuit per unit of time. Because of its definition, it is often confused with the quantity drift speed. Drift speed refers to the average distance traveled by a charge carrier per unit of time.
Like the speed of any object, the drift speed of an electron moving through a wire is the distance to time ratio. The path of a typical electron through a wire could be described as a rather chaotic, zigzag path characterized by collisions with fixed atoms.
Each collision results in a change in direction of the electron. Yet because of collisions with atoms in the solid network of the metal conductor, there are two steps backwards for every three steps forward. With an electric potential established across the two ends of the circuit, the electron continues to migrate forward.
Progress is always made towards the positive terminal. Yet the overall effect of the countless collisions and the high between-collision speeds is that the overall drift speed of an electron in a circuit is abnormally low.
A typical drift speed might be 1 meter per hour. That is slow! One might then ask: How can there by a current on the order of 1 or 2 ampere in a circuit if the drift speed is only about 1 meter per hour? The answer is: there are many, many charge carriers moving at once throughout the whole length of the circuit.
Current is the rate at which charge crosses a point on a circuit. A high current is the result of several coulombs of charge crossing over a cross section of a wire on a circuit.
If the charge carriers are densely packed into the wire, then there does not have to be a high speed to have a high current. That is, the charge carriers do not have to travel a long distance in a second, there just has to be a lot of them passing through the cross section. Current does not have to do with how far charges move in a second but rather with how many charges pass through a cross section of wire on a circuit.
To illustrate how densely packed the charge carriers are, we will consider a typical wire found in household lighting circuits - a gauge copper wire. Each copper atom has 29 electrons; it would be unlikely that even the 11 valence electrons would be in motion as charge carriers at once.
If we assume that each copper atom contributes just a single electron, then there would be as much as 56 coulombs of charge within a thin 0.
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