What is an ohm and what is Ohms Law?

An Ohm is the SI unit for electrical resistance and is symbolised by the Greek letter Ω. 

The Ohm is related to the current and voltage in a system: a current of 1 amp through 1 ohm of electrical resistance produces a voltage of 1 volt across it. 

The formula for this is I=V/R where:

I = the current through the conductor

V = the voltage measured across the conductor

R = the resistance of the conductor

In respect to resistance, it is a measure of the opposition to current flow in an electrical circuit.  There is no such thing as a perfect conductor, so as a perfect conductor is defined as a material that enables electrons/charged particles to move freely within it, and we know that there is no perfect conductor, resistance is exactly what it says - opposition to the free movement of electrons/charge.  This opposition leads to losses of power transmitted- where the electrical energy is “lost” and  converted to heat energy.

To understand current in practical terms, it is easiest to consider Ohms law and the 3-way relationship between Voltage (potential difference/PD), Current and Resistance.

Ohms Law

The current in a circuit is equal to the potential difference divided by the resistance of the circuit.

Ohms Law Triangle


To further understand, it is sometimes easier to consider the below:

You can imagine an electrical circuit in a similar way to a water pipe, transporting water from A to B.

What is Voltage, Current and Resistance?

Resistance, as the name implies is the difficulty encountered by the flow of current- if you can imagine water trying to pass through grit/sand, the 2 options would be to a) increase the size of the tube to reduce the resistance or (b) to put more pressure behind the water to force it through the obstacle (resistance)

Current equates to the intensity of electric charge passing through the conductor, so it therefore would mean that the larger the conductor (or bore of a hose) the larger the possible current.

Voltage or PD is the pressure that it takes to move the electricity (or water) - so  we can consider voltage as electrical pressure or more correctly Electromotive force.

The next step is to read more on how this then applies to in calculating losses in cable circuits....


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