How to apply Ohm's Law to series and parallel circuits

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Electronic circuits are examined mathematically to determine if they will function safely and predictably as designed. Ohm’s Law is used to calculate values of circuit components and determine required voltages and currents as well as determine how much power will be consumed when the circuit is energized.

Let’s start with figuring out what Ohm’s Law even is. Ohm’s Law was named after Georg Ohm who discovered that current flow through a conductor is directly related to the voltage and resistance. This means that the voltage can be found by multiplying the current and resistance in a circuit or component.

Examples: V=I x R, R=V/I, I=V/R

Where:

V = voltage

I = current

R = resistance

Now, how do we apply this to a circuit? Well, first we must decipher if the circuit is in series or parallel as each has its own rules to come up with a total for each value. The series equations go as such (C below is capacitance):

VT= V1+V2+...

IT= I1= I2= ...

RT= R1+R2+...

1/CT= 1/C1+1/C2+...

Now let’s go over the equations for a parallel circuit:

VT= V1=V2=...

IT= I1+I2+...

1/RT= 1/R1+1/R2+...

CT= C1+C2+...

What has changed? In a parallel circuit, the voltage total is equal to the voltage in each line of the parallel circuit. Current is added up to find the total. The equations for resistance and capacitance are switched.

These equations are pertinent when planning any circuit, so it is vitally important to learn if you plan to tinker with electronics. Don’t fret, Digi-Key has some online calculators that can help with this. Practice makes perfect. Happy learning!