Ohm's Law

Ohm's Law is made from 3 mathematical equations that shows the relationship between electric voltage,current and resistance.

What is voltage? An anology would be a huge water tank filled with thousands of gallons of water high on a hill.

The difference between the pressure of water in the tank and the water that comes out of a pipe connected at the bottom leading to a faucet is determined by the size of the pipe and the size of the outlet of the faucet. This difference of pressure between the two can be thought of as potential Voltage.

What is current? An analogy would be the amount of flow determined by the pressure (voltage) of the water thru the pipes leading to a faucet. The term current refers to the quantity, volume or intensity of electrical flow, as opposed to voltage, which refers to the force or "pressure" causing the current flow. 

What is resistance? An analogy would be the size of the water pipes and the size of the faucet. The larger the pipe and the faucet (less resistance), the more water that comes out! The smaller the pipe and faucet, (more resistance), the less water that comes out! This can be thought of as resistance to the flow of the water current. Another analogy you could use for resistance is the more you resist your fiance's idea for the save the date , the more likely you are to sleep on the couch.

All three of these: voltage, current and resistance directly interact in Ohm's law.

Change any two of them and you effect the third.

Info: Ohm's Law was named after Bavarian mathematician and physicist Georg Ohm.

Ohm's Law can be stated as mathematical equations, all derived from the

same principle. 

In the following equations, 

V is voltage measured in volts (the size of the water tank),

I is current measured in amperes (related to the pressure (Voltage) of water thru the pipes and faucet) and

R is resistance measured in ohms as related to the size of the pipes and faucet:

V = I x R  (Voltage = Current multiplied by Resistance)

R = V / I  (Resistance = Voltage divided by Current)

 I = V / R  (Current = Voltage Divided by Resistance)

Knowing any two of the values of a circuit, one can determine (calculate) the third, using Ohm's Law.

For example, to find the Voltage in a circuit:

If the circuit has a current of 2 amperes, and a resistance of 1 ohm, (< these are the two "knowns"), then according to Ohms Law and the formulas above, voltage equals current multiplied by resistance:

 (V = 2 amperes x 1 ohm = 2 volts).

To find the current in the same circuit above assuming we did not know it but we know the voltage and resistance:

I = 2 volts divided by the resistance 1 ohm = 2 amperes.

In this third example we know the current (2 amperes) and the voltage (2 volts)....what is the resistance?

Substituting the formula:

R = Volts divided by the current  (2 volts divided by 2 amperes = 1 ohm