Connecting in series

Sometimes the resistance you want is not one you can buy. Two or more resistors joined together will do instead, and there are two ways of joining them. This is the first.

A series arrangement

Connecting resistors so that the whole current flows through every resistor in the circuit is called connecting them in series.

Figure to be added

Figure 19.29 — three resistors R1, R2 and R3 connected in series in a single loop with a cell and an ammeter, the current I marked flowing round the one path available.

There is only one path

Look at the figure and notice there is nowhere for the current to divide. Whatever leaves the cell has to pass through R1, then through R2, then through R3, and back. That is what "the whole current through every resistor" means, and it is the fact the next page builds on.

Two consequences worth naming now

Before any algebra, both of these follow just from having a single path.

The current is the same at every point in the circuit, so one ammeter anywhere in the loop reads it.
Breaking the circuit anywhere stops all of it. In a string of bulbs wired in series, one failure puts them all out.

Series means one path

In a series arrangement there is a single route for the current, so the same current flows through every component in it.