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**Voltage, Current, and Power, Overview:**

Today we will see the concept of electric current, electric voltage and electric power in the electrical circuits. And we will see that how they are related to each other. So, let’s first start with the Electric Current.

**Electric Current: **

So, in simple terms, it can be defined as a flow of electrical charges. So, to understand the current, first of all, let’s see the concept of electrical charge. So if you see any atom which is the fundamental building block of any material, it consists of three primary elements. It contains proton and neutron which resides in the nucleus and the electron moves around the nucleus in the orbits.

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Now, the electron which is moving in the outermost orbit can be easily knocked out of the atom by applying a little bit of energy. And these electrons which are in the outermost orbit contributes in the flow of current. So, these electrons possess a negative charge, while proton possesses a positive charge. Neutrons have a no charge or electrically they are neutral. So the same polarity charges have a tendency to move away from each other. While the opposite polarity charges have a tendency to move towards each other.

**Unit of Charge is Coulomb:**

The unit of the charge is Coulomb. And it is denoted by symbol Q or q. When we talk about the charge of electrons sometimes it is denoted by symbol e. so 1 electron has a charge of 1.6 x 10^ -19 Coulomb. So to have one coulomb of charge, we require 4.28 x 10^18 electrons, which is the inverse of this quantity. So to have one coulomb of charge, we require the charge of these much electrons. So as we have understood the concept of charge, now let’s talk about the concept of electric current.

So, let’s assume that we have a piece of copper wire and electrons are flowing through this copper wire and we want to find out that how many electrons are flowing through this copper wire. So, let’s take one reference point in this copper wire A-A’. That is the cross section of this copper wire. And let’s assume that amount of charge that is flowing through this copper wire is 1 C. So, if 1 coulomb of charge is passing through this reference point in one second, then we can say that the current which is flowing through this copper wire is 1 C/S Or 1 Ampere. So, the electric current can be defined as a rate at which this electrical charge is passing through this reference point. The electric current is defined by a unit of an ampere. And it is denoted by the symbol I. So to understand the concept of electric current, let’s take an example of tap water. The amount of water flowing through the tap depends on the rate at which water particles are coming out of this tap. The higher the rate at which particles are coming out of the tap. more will be the water flow. Likewise, the higher the rate at which this electrical charge or electrons passing through this reference point, the higher will be the flow of electric current. So if 5 C of charge is passing through this reference point in one second, then we can say that the flow of electric current is five ampere.

So to have the movement of this charge, we require some sort of energy. So, these electrons or electrical charge will not contribute to the flow of electric current unless we apply some form of energy or external force. At room temperature, these electrons move randomly in all direction. Because of that net motion of flow is zero. So, to get the net motion of flow, we need to apply some form of energy. So, let’s apply this energy in the form of an external battery, which connected to this copper wire. So because of this battery, the electrons will be supplied to the one end of the copper wire. So, electrons which are free electrons in this copper wire will get repelled with this negative charge which supplied by this battery. And these free electrons will move to the other end of the copper wire and at the other end of the copper wire, they will get attracted to the positive terminal of the battery. So in this way, we get a flow of electrons from the negative to the positive direction. So, the electrons in the circuit flow from the negative to the positive terminal. But in the electrical circuits, if you see, we generally take a flow of current from positive to the negative direction. So that is the conventional flow of current. So, the conventional current flows from the positive to the negative terminal of the circuit. So as we have discussed, to get movement of this charge we require some sort of energy. And that energy is measured in the units of a joule. So, let’s assume that we have one coulomb of charge and to move this charge from negative to the positive terminal, we require energy. That is one joule. So if 1 Joule of energy is required to move 1 C of charge from negative to the positive terminal then we can say that the potential difference between the positive and the negative terminal is 1 volt.

**Electric Voltage: **

So, the electric voltage can be defined as an energy required or work done to move a unit charge from one point to the another. So, let’s say we have two points A and B and at point A, we have 2 C of charge. So to move a 2 C of charge from one point A to the B, let’s say we require a 2 Joules of energy. So, electric voltage or potential difference between this point A and B can be defined as 2 J/2C, that is 1 Volt. The unit of this potential difference or electric voltage is VOLT and it is denoted by symbol V. So the higher the amount of energy required to move a charge from one point to the another point, the higher will be the potential difference. So, let’s say if 5 C of charge is at point A and to move this charge from point A to the point B, let’s say we require 50 J of energy. So the potential difference between the points will be 50 J/5C = 10 Volt. So to understand this concept.

Let’s take one example. Let’s say we have one ball on the ground and it’s weight is 100 grams. Now, we want to throw this ball from the ground to the top of this building, which is having a height of 10 meters.

So for this task, we require some energy. Let’s say for this task we require energy E1. Now in another case, we have a ball with the same weight or mass that is 100 gram and we want to throw this ball to the top of one building which is having a height of 20 meters. So for that let’s say we require energy E2. Now, here energy E2 will be definitely greater than the E1. Because the height in the second case is more. So the amount of energy required in the second case will be the more. So, we can compare this example with the electric voltage. The higher the difference between the two points or higher the height of the building, higher the amount of energy is required to throw a ball. Likewise, the higher the potential difference between the two points, more amount of energy is required to move a charge from one point to the another point.

**Electric Power:**

So the Electric Power can be defined as the rate at which energy is supplied or consumed in the system. So this electric power is denoted by symbol P and mathematically, it can be written as E/t. That is the rate at which energy supplied or consumed in the system.

So it is defined by unit Joule / Second Or Watt. While in the earlier case, Electric Voltage mathematically can be written as V= E/Q. That is the energy required to move a unit charge and the electric current I can be defined as rate at which electrical charge is moving from the reference point, that is Q/t.

Now as we were talking about the electric power, P= E/t. So, let’s understand the concept of power by taking one simple example. Let’s say we have one coulomb of charge at point A. We want to move this charge from point A to the point B. And the energy required for this task is let’s say 5 Joules and the time required for this task is let’s say 5 seconds. So, by the definition of the electric power, P that is defined by the rate at which energy is consumed. That is E/t. Now here, in this case, to move 1 coulomb of charge, we require 5 Joules of energy. That is 5 Joules of energy per 1 Colomb. And the time required to move this 1 Coulomb of charge is 5 seconds, That is 5 seconds / 1 Coulomb. So the electric power required for this task is 5J / 5 seconds, that is 1 watt. Now, let’s generalize this term. Let’s say we require E joules of energy to move Q amount of charge and the time required for this task is t. That is t seconds for Q coulomb of charge that is electric power. So we can rewrite the term like, (E/Q) * (Q/t) So E/Q is nothing but Voltage, as voltage can be defined as the energy required to move a unit charge. And I, that is electric current can be defined as the rate at which the charge is moving. So, we can write power as a product of V*I.

So, electric power can be defined as a product of V*I. So, this is very useful relationship between the electric voltage, electric power and the electric current. Now in electrical circuits, the power is either consumed or it is been supplied. So in electrical circuits, if you see any element is either dissipating power or supplying a power. So, how to know that element is supplying a power or dissipating a power. This can find out by the simple sign convention, So we will use this sign convention, to know whether this element is supplying energy or it is dissipating energy. So let’s say we have one element and the voltage between the two terminal is V. So if the electric current is flowing out of the positive terminal of that element then we can say that that element is supplying a power Or if the current is flowing into the positive terminal of that element then we can say that that element is dissipating a power.

So, let’s take one example to understand it very clearly. Let’s say we have two voltage sources, which are connected through one resistor. We have one voltage source of 5V, and another voltage source of 3 V. They are connected by one resistor R. So, the current will flow from higher potential to the lower potential, like water flows from the higher elevation to the lower elevation. So, we will have a current in a clockwise direction. And because of the flow of electric current, there will be a potential drop across this resistor R. Let’s say that is Vr. Now, lets apply a sign convention across all elements. So across the 5 volt source, the current is flowing out of the terminal that means, this element or this source is supplying a power. Now, let’s see a resistor, So the current is entering into the positive terminal of the resistor. So the power is dissipated across this resistor. Now, let’s see across this 3 V voltage source. So across 3 V, current is entering into the positive terminal. So this 3 V source is also dissipating an energy or power. So 5V is supplying energy and the resistor and 3V voltage source is dissipating the energy or power. So by using this sign convention method, in any network, we can find which elements are supplying the power and which elements are dissipating the power.

So let’s summarize what we have studies in this article. We have seen the electric current, electric voltage and electric power in the electrical circuits and how they are related to each other. They are related to each other by this P= V*I relationship. So, hope you understood what current, voltage is and power in the electrical circuits.

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