DC Circuits
RESISTORS IN SERIES
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
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Example Problem on Resistors in Series
Continue to:Resistors in Parallel
Self Test
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