What is Ohm's Law?

Cartoon Illustration Of Ohms Law

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points.

Ohms Law Pyramid

The relationship between voltage, current, and resistance is described by Ohm's law.

i = v/r

Where;
i = Current measured in Amp
v = Voltage measure in Volt
r = Resistabce measure in ohms \Omega 

The equation, tells us that the current, i, flowing through a circuit is directly proportional to the voltage, v, and inversely proportional to the resistance, r. In other words, if we increase the voltage, then the current will increase. But, if we increase the resistance, then the current will decrease. We saw these concepts in action with the garden hose. Increasing the pressure caused the flow to increase, but getting a kink in the hose increased the resistance, which caused the flow to decrease.

The way the equation is written here, it would be easy to use Ohm's law to figure out the current if we know the voltage and the resistance. But, what if we wanted to solve for the voltage or the resistance instead? One way to do this would be to rearrange the terms of the equation to solve for the other parameters, but there's an easier way. The diagram above will give us the appropriate equation to solve for any unknown parameter without using any algebra. To use this diagram, we simply cover up the parameter we're trying to find to get the proper equation.

Here is a real illustration of Ohms law: Pressure, resistance and flow of water flowing via pipe or hose:

Pressure, Resistance, and Flow

Photo credit: Cleaning and Sealing

This past weekend, I was out in the garden watering the flowers when suddenly the flow of water nearly stopped. I looked behind me and realized there was a kink in the hose that was restricting the water flow. After I straightened out the kink, the water flow came back and I resumed my watering. But, a few minutes later, the water flow slowed down again. I looked for another kink in the hose, but this time I couldn't find one. I went in the house and found that my roommate was taking a shower while running the washing machine and the dishwasher all at the same time! Our water pump couldn't keep up with so much demand for water, and as a result, the water pressure to my garden hose had dropped, which reduced the water flow.

This got me thinking about how similar water flowing through a hose is to electric current in a circuit. Just like the water flow was determined by the amount of pressure and resistance in the hose, electric current is determined by the amount of voltage and resistance in an electric circuit.