There is no doubt about the importance of electrical energy as a concept in science. Unfortunately, the concept is often misunderstood. Here, we will explain the definition of the concept, provide examples of how the energy is utilized and explain how the energy works to help make it clear.
To make the concept easier to understand, we will also explain various things related to it. For instance, the units of measurements and symbols used for the energy, what is a Joule, relations to voltage, Ampere and Watt.
Electrical Energy Definition
Energy is defined as the capacity or ability to work and it has many forms and electrical energy is one of them. This form of “ability to work” is the result of the flow of electric charge, hence the ‘electrical’ name. It can be either potential or kinetic albeit it is typically encountered as potential energy.
In its potential form, this energy is derived from the relative positions of charged particles. These charged particles can move from one point to another through a medium. The movement of these charged particles through a medium (like wire, for instance) is known as current electricity.
Static electricity, which is another example of electrical energy in potential form, is caused by the imbalance between an object’s positive and negative charges. If the charge is sufficient, the energy may be discharged thus forming a spark. This is the energy in its kinetic form.
The direction of an electric field is always shown moving from positive to negative. This is the general convention and not how the most common current carrier, which is a negative particle or electron, moves. In fact, a negative particle or electron moves from negative to positive.
Electrical Energy Example
There are many examples around us. For instance, when we turn on the switch of a light bulb, the electrical energy (in its potential form) is used to power the light bulb. This converts the electric potential energy to heat and light.
Another example is a battery. Unlike a light bulb where the electrical charges are in the electrons in a metal, a battery’s electrical charges are in the ions in its solution. The principle is the same: electric potential energy is turned into another form of energy.
The followings are also examples of electrical energy:
- Direct current or DC circuit
- Alternating current or AC circuit
- The energy that electric eels generate
How Does It Work?
The movement of an electron is governed by attractive forces and repulsive forces. Attractive forces occur when two opposite charges meet. For example, when electrons meet protons. Repulsive forces occur when two same charges meet. These two forces are manipulated to generate electrical energy.
Using electrons as an example, this is how the energy works:
- a charged particle (in this case, an electron) has an electric field surrounding it
- the field exerts a force on other charged particles
- the exertion force causes the charged particle to move
- the movement causes the charged particle to “do work”
Note that the charged particle doesn’t have to be an electron. It can also be a proton, atomic nuclei, positively-charged ions (cations), negatively-charged ions (anions), positron and so on.
Units of Measurements and Symbols
Volt (symbol: V) is the SI unit of measurement for the unit voltage or potential difference. Volt is just one among other units of measurements and symbols for electricity. Below are quantities with their units of measurements and symbols:
- Electric current (I), unit: Ampere or amp, symbol: A
- Electric charge (Q), unit: Coulomb, symbol: C
- Electric power (P), unit: Watt, symbol: W
- Energy (E), unit: Joule, symbol J
- Alternatively, unit: kilowatt-hour, symbol: kWh
- Resistance (R), unit: Ohm, symbol: Ω (omega, pronounced “Ohm”)
- Capacitance (C), unit: Farad, symbol: F
- Inductance (L), unit: Henry, symbol: H
What Is a “Joule”?
As explained earlier, energy is the capacity or ability to do work. The standard unit of to measure energy is Joule. The standard unit Joule is also used to quantify the amount of work done on an object. As a unit of energy, 1 Joule equals 1 kg.m2.s-2. As work, a Joule equals 1-newton meter thus 1 J = 1 Nm.
Here are examples to put “What is a Joule” into perspective:
- 1 Joule is the amount of energy required to lift a medium-size tomato up one meter. If the tomato is dropped from the same spot, which is one meter high, the energy released is equal to a Joule.
- 1 Joule is the amount of electricity required to turn on a 1W LED lamp for a second.
- A tennis ball moving 6 meters per second has a kinetic energy of 1 Joule
Relations to Voltage
In electrical terms, a Joule of energy is the amount of energy expended by 1 ampere at 1 volt in 1 second. Movement of electric charges around a circuit results in electric current. This movement can only happen if there is a force to do the work moving the charges from one node to another and that is the voltage.
Voltage is defined as the potential difference between two points. However, there is more about voltage than this definition. Voltage can also be defined as the work needed to move a single Coulomb of charge from point A to point B.
Formula and Examples
The relationship between electrical energy and voltage can be put into a formula. The formula goes like this:
V = J / C, where
- voltage is in volts
- energy is in Joule
- charge is in Coulomb
Let’s say if the energy is 1 Joule and the charge is 1 Coulomb, then
V = 1 / 1
V = 1 or 1 volt
Let’s use another example. Suppose there is a battery that expends 135 Joules to move 15 Coulombs around an electrical circuit. What is the battery’s terminal voltage?
Since V = J / C, therefore
V = 135 / 15
V = 9V
In other words, every Coulomb of charge carries 9 Joules of energy
Relations to Ampere
As we mentioned in the early section, the symbol of electrical charge is Q. Coulomb is the unit of electrical charge. The flow of electrical charge around a circuit represents a flow of current. Thus, Q equals 1 Coulomb of charge or 1C. Q can be either positive (+Q) or negative (-Q).
The flow of charge in the forms of electrons around a closed circuit is known as an electric current. The “flow” here implies movement. Which means to create an electric current the charge has to move. What makes the charge move? The answer is voltage, which we have explained in the previous section.
The potential difference between two points in the circuit provides the needed electrical energy to move charge (as electric current) around the circuit. Due to this, the two points have to have a potential difference as without which, there won’t be any movement of charge, which means no current flow.
If the movement of charge is an electric current, then current can be defined as the rate of movement of the charge. We can find the electrical current’s strength current by selecting a point and measure the amount of charge that flows past the selected point in one second. This will get us the electrical current strength in Amperes.
If put into a formula, it goes like the following:
I = Q / t, where
- I is the electric current
- Q is the electric charge
- T is the time
Triangle for Formulas
To make the formulas easier to memorize, we can use a triangle. This triangle is divided into three parts: one part at the top and the other two at the bottom. The top part is Q and the bottom parts are I and t. The relationships between the parts are like this:
- The top part can be found by multiplying the bottom parts. If put into a formula, Q = I x t
- An unknown bottom part can be found by dividing the top part by the known bottom part. If put into a formula, the formula is either I = Q / t, (where t is known) or t = Q / I, (where I is known)
This triangle is similar to the formulas of Ohm’s law. The law states that a circuit’s voltage can be found by multiplying the circuit’s current and resistance. Ohm’s law has other uses, including to calculate the current fractions in a current divider or the voltage fractions in a voltage divider, among others.
- Let’s say that the electric charge is 1 Coulomb and it takes 1 second for it to past a given point. The electric charge is
I = 1C / s
1A = 1 C / s
From this, we find that 1A of current is equal to 1C of charge that flows past a given point in one second. The more charge per second moves past the point, the greater the current will be.
- Let’s use another example. If there are 450 Coulombs of charge flows through a given point in a circuit in 1.5 minutes, how much is the current flow?
Since I = Q / t, therefore
I = 450 / (1.5 x 60)
(note: the time must be converted into seconds)
I = 450 / 90
I = 5A
The current flow is 5 Amperes.
- Suppose in a circuit there are 6 Amperes of current flowing through a resistor. How much is the electric charge that will flow through said resistor in 60 seconds?
Since Q = I x t, therefore
Q = 6 x 60
Q = 360C
The electric charge is 360 Coulombs.
Relations to Watt
Another related concept to electrical energy is electrical power or Watt. Electrical power is derived from two quantities: current and voltage. So it follows that electrical power can be defined as the rate at which work is done in expending energy.
In the previous two sections, we explained that voltage is the amount of works (in Joule) required to move 1C of charge from point A to point B and that current is the rate of movement of the charge. If we relate these to electrical power, it goes like the following:
If V = J / C and I = Q / t, where
- V is voltage
- J is energy
- C is electric charge
- I is electric current
- Q is electric charge
- t is time
then electrical power (P) can be defined as the multiplication of the two qualities.
If put into a formula:
V = J / C and I = Q / t
Since P = V x I, then
P = J / C x Q / t
as Q = 1C, then
P = J / C x C / t
P = J / t
This proves that electrical power can be defined as the rate at which work is done in expending energy. In other words, 1 Joule of energy used in one second.
The unit of measurement for electrical power is Watts, but since P = V x I is equal to P = J / t, we can say that 1 Watt is equal to 1 Joule per second. Since work is equal to power times time, we can also say that 1 Joule is equal to 1 Watt per second.
Let’s use an example to make the formulas P V x I = J / t clearer. Suppose a 200 Watt light bulb is switched on for 30 minutes. How much energy in Joules is required by the light bulb for the duration it is switched on?
If J = P x t, where
- J is energy
- P is electrical power
- t is time
J = 200 x (30 x 60)
(note: the time is converted to second)
J = 200 x 1800
J =360,000 or 360kJ
The energy is 360,000 Joules or 360 kilojoules When dealing with Joule as an electrical energy unit, it is a lot more practical to use kilojoules. A Joule is a small quantity just like a Watt is, which is why its larger presentations (kiloJoules, megajoules, and so on) are more practical.