A Simple Explanation Of Ohm’s Law

Ohms LawIf you’ve spent time reading about electronics or DIY you’ve likely run into Ohms Law as it is one of the most fundamental building blocks to understanding how electronics work and designing circuits. The above diagram may even be familiar to you. But what does it all mean? Today I’d like to spend some time exploring Ohms Law to provide you with a greater understanding of the principal and of electronics as a whole.

Ohms Law describes the relationship between three basic elements of a circuit, The Voltage (V), Current (I) and Resistance (R) and shows how each of these values are interconnected.

The most common analogy used to describe this principle is to visualize a series of pipes with water flowing through them. Each of these values can be associated with a characteristic of the pipe system.

  • Voltage – The force with which water is being pumped into your system, with electronics we can modify this by using higher voltage (or more) batteries or a higher voltage power supply.
  • Resistance – The factors which restrict water flow through the pipe, for instance the width of the pipe or a partial cutoff valve. Resistance in a circuit can be added using resistors of various types
  • Current – The speed at which water which flows through the pipe

Imagine if you had two sets of pipes which are identical width and length. But you attached them to different pumps, one of which had double the force of the first. The resistance against the water would be identical (Pipe Size) but because the voltage (pump strength) is higher on the second set of pipes the water will move much faster through it causing it to have a greater current. In order to make the current the same between the two we would either have to adjust the voltage (Pump Strength) of one of the pipes to make them equivalent or adjust the resistance (Pipe width) to make up for the difference.

Adjusting the resistance would balance out the difference in voltage allowing the same amount of water to flow.

Lets try a real world example. Lets say I have a light bulb which runs off 1 ampere (Current) and I have 2 AA batteries in series giving me 3V of power. How do I decide what value of resistor to use to complete the circuit?

Using Ohms law we know that R=V/I, which we can substitute the values from the above example to complete :

R = 3/1
R = 3 ohm

From here you can take a 3 ohm resistor off your shelf, plug it into the circuit and you are in business!

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