Resistors can be connected in series; that is, the current flows through them one after another. The circuit in Figure 1 shows three resistors connected in series, and the direction of current is indicated by the arrow. |
Figure 1 Resistors connected in series. |

Note that since there is only one path for the current to travel, the current through each of the resistors is the same.

**[1]**

Also, the voltage drops across the resistors must add up to the total voltage supplied by the battery:

**[2]**

Since **V = I R**, then

**[3]**

But Ohm's Law must also be satisfied for the complete circuit:

**[4]**

Setting equations [3] and [4] equal, we get:

**[5]**

We know what the current through each resistor (from equation [1]) is
just
**I**.

**[6]**

So the currents cancel on both sides, and we arrive at an expression for equivalent resistance for resistors connected in series.

**[7]**

In general, the equivalent resistance of resistors connected in series is the sum of their resistances. That is,

**[8]**

This can also be written in terms of conductances, since conductance is just the reciprocal of resistance:

**[9]**

Here is an interesting interactive exercise to help you with this concept
and the use of Ohm's Law

Use the "BACK" button to return to this place when you are finished.

Press here

Example Problem on Resistors in Series

Continue to:Resistors in Parallel

Self Test

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