Ohm's Law (V = IR)

In the first half of the nineteenth century a German scientist named Georg Ohm performed many experiments which resulted in him being able to show that there is a mathematical relationship which links current, voltage and resistance.

In the days when he was performing his experiments there were no meters as we know them today. Only after considerable effort and at the second attempt did he manage to devise what we know today as Ohm's Law.

Ohm's Law is one of the most fundamental and important laws governing electrical and electronic circuits.

It links

the current I flowing though a device (measured in amps (A),

the potential difference V across it (the voltage - measured in volts (V)) and

its resistance R ( measured in ohms represented by Ω (the Greek letter Omega))

If two are known, the third can be calculated.

How to use the Ohm Triangle

You 'cover' the unknown value with your finger = the triangle then shows you how your two known values are related,

Here we can see that I = V/R
Here we can see that R = V/I
Here we can see that V = IR