Musings on Voltage and Current

Getting the basics right

There is a reason why 'science is science'. At the root of science are experimentally verifiable principles based on a set of laws. There is a method to the madness, and even at the elementary level. And the hardcore laws surrounding electricity, the phenomena arising from the elemental particle electron, is associated with electric charge. There are two main heroes in the story of electricity and they are Voltage and Current. These are the building blocks for Energy, and its important to understand the basics before talking about battery energy.

Voltage-the force

The idea surrounding the concept of Voltage is that, the electric charge creates a force field around it, called the electric field. Its pretty similar, and actually associated with the lines of field that is created by a magnet. If you have two locations which differ in the amount of free electrons, then the electric charges associated with the locations are different and correspondingly the field created by is different. The location with more concentration of electric charges has a higher potential of the field, and is called as the negative terminal. The higher potential is negative here, because the charge associated with the electron is considered as the basic negative charge. As physics is about symmetry and balances, there is also a lower potential, and an associated positive terminal. And you have seen the plus (+) and minus (-) signs indicating these regions in a battery, and a pictorial representation of these fields is below.

In fact, battery is central to the development of Voltage, as it is a moniker attributed to a stalwart, Alessandro Volta, developer of the first chemical battery. The unit for Voltage, Volt also comes from Volta. What Volta did, is simply to separate two different metal plates in a solution. He discovered the potential difference between the plates because of the inherent difference in property of the metals which we call as Voltage now. This force will induce the electrons to flow from one metal plate to another, making it into a battery. And there you have it, Voltage is simply that. It is the force, very much like the pressure difference which causes water to flow.

Current: the rate of flow

The next thing to tackle is the flow of electrons, the current. The core idea is surrounding current is that in nature everything tries to balance out. That is the end goal of the flow is to balance out the potential difference. And as you would expect it, the flow of electrons happens from the higher potential to the lower potential, that is from the negative (-) terminal to the positive (+) terminal. One catch, here is that though the actual electron flow is from negative to positive, current is assumed to be in the opposite direction, that is from positive direction as shown in Image 3. This is because historically somehow it was arbitrarily assumed to be so.

Now you know why arrows are flowing out of the positive terminal in Image 2, though electron is travelling in the opposite. The current is defined the rate of flow of the charge, that is there is an attribute of time associated with it. Current is measured in terms of how much charge passed in a second of time. The unit for current, Ampere, named after another great physicist Andre Marie Ampere.

Ampere hour and Ampere second

In case you are wondering, if there are units to measure how much charge is flowing, there are a couple. The difference between them is the period of time, i.e. second or hour. The scientific unit is Coulomb, which is actually the basis of definition of Ampere. The time period associated for this amount of charge a second, and one Coulomb is one Ampere Second. Coulomb is a amount of charge that comes from approximately 6.2 billion billion billion electrons. I know that is a lot of zeros, but don't worry, its only because the elemental charge associated with an electron is very minuscule.

If it comes to a battery, another term is used to describe 'how much' charge. This unit is Ampere Hour, that is the amount of charge if one Ampere current is flowing for an hour. We should remember that an chemical battery is a storage unit for charges. Current, or charge flow happens only because there was enough charge stored in it to begin with. And an hour is a more appropriate period of time to prescribe the amount of charge stored in this case. An ampere hour is a much bigger unit, it is 3600 times of a Coulomb The significance of Ampere hour unit is that, an hour comes quite handy when we have to account for the energy associated with the charge stored. I will try to explain that in the next section.

Energy

The concept of energy is also associated the principle of balance of nature. The law of conservation of energy says that we cannot create or destroy energy, merely transform it. What happens in electricity is that electrons flow because of a force field. So to quantify energy I need to see how much flow happened because of the force. That means if we multiply amount of how much flow is happening, with the force that is causing it, we get the energy.

• Energy = Force x Flow = Force x Rate of Flow x Time

We know for electrical energy

• Force= Voltage and
• Rate of Flow= Current
• Therefore Electrical Energy = Voltage x Current x Time

To define a unit for electrical energy let's assume Voltage is 1 Volt, Current is 1 Ampere, and Time as 1 hour

• Watt hour = 1 Volt x 1 Ampere x 1 hour = 1 Volt x 1 Ampere Hour

Battery Voltage and Capacity

If I am talking about batteries, I need a unit to express how much charge is stored in it. You already know you need to store charge to take charge out. The process of taking out or removal stored charge from a battery is called discharging. It makes practical sense for me to tell a person how much energy they might be able to take out in an hour. For this I need to first find battery Voltage

Battery Voltage

The voltage a battery creates is pretty much dependent on the inherent properties of the material used to create the battery. If I use Nickel and Cadmium, I get a potential difference of 1.2 Volt.

The material need not always be a metal, it could be any conductive mixture. For example if I were to create a battery with Lithium Iron Phosphate on one side and graphite on another side I get a potential difference of 3.2 Volt.

Battery Capacity

So now as I know the Voltage, all I need to express battery energy is the 'flow'. If I use Ampere Hour to express the amount of stored charge, it will give me an indicator of how much energy I can take out in an hour. This also helps me to correlate it with Watt hour, which is the common unit for electrical energy consumption. All I need to do is to multiply the Voltage with the Ampere hour.

What about battery power capacity

We only talked about energy till now, we also need to talk about the power. Power is about the rate of flow was achieved from the force. The difference between power and energy is that the former is an instantaneous concept without any implication of time. So power can be calculated from the same force and flow, ignoring the time angle.

• Power = Force x rate of flow
• Electrical power = Voltage x Current

Assume a our Nickel Cadmium battery is supplying 1 Ampere current.

• So our battery power capacity = 1.2 Volt x 1 Ampere = 1.2 Watt

If I had to calculate power for the Lithium Iron Phosphate and Graphite battery, if it were supplying one Ampere current, it would be 3.2 Watt.

End note

As I have explained in my blog post on power factor, power is pretty much about how loud I can sing. I am truly hoping this time that my voice is powerful and loud enough. Though I am an awful singer, I am a true believer of doing no harm by teaching. I hope I can reach the hearts of people who feel its okay to write that "Voltage is the way of describing energy from one electron, where as Watt hour is the way to describe energy from all electrons".

Simply put, the Voltage or the force arose because of all the electrons. This is the reason why terminal Voltage of a battery falls as its total charge reduces. Moreover, Voltage is only a force, and not a descriptor of energy by itself. Specifically with respect to a battery, Voltage is a by product of the material the battery is made from. Let me know if agree with me or not.