What is an Ohmmeter – A Simple, easy to understand guide.

In a nutshell, an Ohmmeter is a device that enables you to measure the resistance inside an electrical component.

What does electrical resistance mean?

Electrical resistance is found in everything that is electrical, such as electrical wires, bulbs switches etc. Electrical resistance slows down the flow of electricity and can even stop the flow of electricity if the resistance is very high. Electrical Resistance is similar to the resistance you get in a water pipe. Water will flow easier and faster when the pipe is big, but if a pipe is small, not as much water can flow through the pipe at the same time, therefore the flow of water is slower. The electrical resistance is like the water pipe and the flow of water is like the flow of electricity.


Ohm’s law in no uncertain terms

Ohm’s law is a law that comprises of 3 parts:




These three parts of Ohm’s law are the three basic units used with electricity. This law shows that these three units are related to one another. There are three equations in Ohms’ law and these equations can be used to find out what the resistance, current and the voltage of a circuit.

The diagrams below show 2 formula triangles for Ohms’s law:

voltage pyramid












These are the three equations that can be extracted from these formula triangles:

Voltage = Current (Amps) x Resistance (Ohms)

Current (Amps) = Voltage ÷ Resistance (Ohms)

Resistance (Ohms) = Voltage ÷ Current (Amps)

These equations show that all three units have a relationship between them. When you know 2 values of these equations, you will be able to find out the third value of the equation.

Resistance works slightly differently to voltage and current because in a circuit, when the resistance goes up the current and the voltage go down and when the resistance goes down the current and voltage go up. This means that resistance always does the opposite to what the current and voltage does.



The Ohmmeter- How it measures resistance.

When voltage is found, you will also find current. An example of this is like water in a river. The water is like the current and voltage is like the flow of water. Water in a river is always flowing but the speed at which the water flows varies. When two values are known, the third unknown value can be found. The way the ohmmeter measures resistance is that it creates a small voltage on the test piece. As mentioned before, voltage will be accompanied by current. Therefore, if the current and voltage is known, the value of resistance can be worked out. The ohmmeter will automatically calculate this value (resistance)  by using the equation : Resistance (Ohms) = Voltage ÷ Current (Amps)


Should you buy an Ohmmeter?

An Ohmmeter goes hand in hand with both an ammeter and a voltage meter, so you’ll need an ohmmeter as much as an ammeter and a voltage meter.

One type of professional that will need to use an ohmmeter is an electrician. Finding the resistance of a circuit or any electrical component is something an electrician needs to do all the time. If an electrician is not able to measure resistance, then they won’t be able to carry out any work relating to circuit resistance and resistance of components of electrical equipment.

Similarly, technicians need to use an ohmmeter to carry out various types of tests. An ohmmeter is an essential tool for them, without it, they too won’t be able to carry out many of the tasks they need to perform.

If you are not an electrician or a technician but you need an ohmmeter to test switches  and identify problems in cables and equipment around the house,then the best option is to buy the low spec, cheaper Ohmmeters. These type of ohmmeters will easily be able to carry out simple tasks like the ones mentioned before, so it is not necessary to invest in the more expensive ohmmeters.

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