Series Circuits



  1. a number of things, events, or people of a similar kind or related coming one after another.

So given the above definition, a series circuit is when there’s only a single path for current to flow. Any break in the wiring or a faulty load will stop current throughout the entire series circuit.

A load is anything in the circuit that does useful work, like the lightbulb in the example below. The inexpensive and/or old Christmas lights have this downfall. When a single bulb burns out, the entire string of lights goes out.

No flow = no go

Rules of a Series Circuit

  • Rule 1: Current is the same throughout the circuit

Since current stays the same through the circuit, this makes calculations using Ohm’s Law easier.

Each component in a series circuit has the same current flow.

I total = I 1 = I

  • Rule 2: The total resistance of a series circuit is equal to the sum of the individual resistances.

Adding the individual value of each component in a series circuit will give the total resistance of the circuit.

In the above example, we have two values.

R total = R1 + R2

R total = 5 Ω + 5 Ω

R total = 10 Ω

  • Rule 3: The total voltage drop in a series circuit is equal to the applied voltage of the circuit.

The total voltage drop across each resistor must add up to the total voltage supplied to the circuit from the battery.

V total = V 1 + V 2

V total = 6 V + 6 V

V total = 12 V

Using Ohm’s Law any of these totals can be found as long as you have at least 2 values.


E = I x R

E = 1.2 A x 10 Ω

E = 12 V


R = E / I

R = 12 V / 1.2 A

R = 10 Ω


I = E / R

I = 12 V / 10 Ω

I = 1.2 A

If at any point there’s a break in the wiring or a load is faulty, no current will flow. No flow = no go.

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