Want to learn more about electricity? Well then, you will need to learn about voltage, current, and resistance, and the different roles they play in an electrical circuit.
TL;DR Voltage is the measurement of "pressure" in an electrical system, measured in Volts. Current is the rate of electrons passing through a point, measured in Amps. Resistance is the measurement of the opposition to current flow in a circuit.
These concepts can be super challenging to grasp as voltage, current, and resistance aren’t visible to the human eye, but they are more theoretical concepts with we have to try and visualise.
But things get easier when you start with understanding what electricity is. Simply put, electricity is the movement of electrons, and since moving electrons create a charge, the movement of electrons can be harnessed to do work.
Simple devices like lightbulbs and sophisticated electronics such as computers and phones all function because of the movement of electrons.
Voltage, current, and resistance can all be described in terms of the movement of electrons. Let’s begin by understanding what voltage is.
The Difference And Comparison: Voltage Vs Current
In short, voltage is the “pressure” force in a circuit. More specifically, it’s the measurement of the potential difference in energy between two points. Current is the measurement of the amount of electrons flowing through a point in the circuit, per second.
What Is Voltage?
Getting a grasp of voltage definition is the first step to understanding how appliances work. In any circuit, electrons move from the negative end to the positive end of the source.
Voltage is the pressure with which the power source pushes the electrons through the circuit.
It is measured in volts (SI unit “V”) as the difference in the charge between two points of the circuit. In the early days of electricity, voltage was called electromotive force (emf), which is why voltage is represented by “E” in equations such as Ohm’s Law.
Voltage is termed after Alessandro Volta, an Italian physicist that invented the voltaic pile, which evolved into the modern-day household battery.
Voltage is used interchangeably with the term “potential difference,” which is defined as the difference in potential energy between two points. In other words, voltage is thought of as a measure of electric potential between the two points in the circuit.
It’s important to remember that the energy difference can only be measured between two points. Without reference to the two points in the circuit, the voltage cannot be defined.
The quantity of this difference helps determine the amount of work the circuit can do. For instance, the typical AA battery has a potential difference of 1.5V. In contrast, the power outlets in homes offer a potential difference of 120V.
Since power outlets have a higher “pressure” of electron movement, they can power bigger appliances than the AA battery.
How Is Measuring Voltage Useful?
Voltage is most commonly measured to troubleshoot circuits.
Circuits are built with the primary purpose of delivering energy to some load. The load may be as small as a household appliance or as large as an industrial machine.
Technicians understand how a circuit should be performing because the voltage and current of the circuit are always mentioned on the load. If there’s no nameplate on the circuit, manufacturers include a detailed schematic of the circuit to help technicians repair it correctly.
The numbers on the nameplate or manual help technicians understand what readings they should expect from the circuit. Measuring the voltage with a multimeter helps the technician objectively understand what the issue may be.
How To Measure Voltage In A Simple Circuit?
A multimeter or voltmeter are the best tools to use when measuring voltage.
- Before you turn the digital multimeter (DMM) on, connect the black lead into the negative socket, and plug the red lead into the positive socket.
- Switch the DMM on, and set it to accommodate for the largest value you expect from the circuit. But bear in mind that it’s best practice to set the DMM to the largest value it can measure.
- Touch the black lead to the lower voltage point, and the red lead to the higher voltage point.
- You may need to adjust the range switch to get the most accurate reading possible. However, some digital multimeters have an auto-ranging feature that removes the need for you to do this.
- You will see the voltage reading appear on the multimeter.
Measuring the voltage of simple circuits is as easy as that. But to measure the voltage in more advanced circuits, you must understand what is applied voltage.
Just like you can measure the voltage across the circuit, you can also measure the voltage across a component in the circuit. The voltage across a component is a lower voltage that is reduced by the internal resistance of said component.
On the other hand, the applied voltage is the voltage that is supplied to the component.
Knowing this difference, you will be able to make sense of the voltage differences at different points of the circuit.
How Current And Resistance Is Related To Voltage?
The current and resistance in a circuit are the rate of flow of electrons and the friction against the flow of electrons at that point in the circuit, respectively.
Current is measured in Amperes (A), which is a unit named after Andrè-Marie Ampére. In equations, the current is denoted by “I.” check out our in-depth article about what size resistor for your Led.
On the other hand, resistance is measured in ohms (Ω), a unit named after Georg Simon Ohm. He is credited for finding the relationship between voltage, current, and resistance in what is known as Ohm’s Law. In equations, resistance is denoted by the letter R.
Ohm’s Law states that the current flowing in a given circuit is directly proportional to the applied voltage in the circuit and inversely proportional to the resistance in the circuit. It’s important to note that for this Law to apply, the temperature must remain constant.
Current in Amperes = Voltage (in Volts) Resistance (in Ohms)
Or
I = V/R
Here’s how you should conceptualize this:
Suppose the voltage in the circuit increases, the current in the circuit will also increase. On the other hand, if the resistance in the circuit increases, the current in the circuit will decrease.
We can use the ohm’s law equation to determine the value of current, voltage, or resistance if we have the two other corresponding values.
To solve for voltage, the ohm’s law equation can be rearranged like so:
Voltage = Current * Resistance
And to solve for resistance, the ohm’s law equation can be rearranged like so:
Resistance = Voltage / Current
Final Thoughts
Voltage current and resistance are the building blocks of electrical systems, and they concepts you will need to understand if you want to build anything electrical, or to just understand how the power sockets in your house works.
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