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Starting electronics
Back to the circuit: it’s now time to measure the overall resistance
of the series resistors. Following the same instructions
we gave you before, do it!
If your measurement is correct you should have a reading of
20 k. But what does this prove? Well, it suggests that there is
a relationship between the separate resistors (each of value
10 k) and the overall resistance. It looks very much as though
the overall resistance (which we call, say, R OV
) equals R1 +
R2. Or put mathematically:
But how can we test this? The easiest way is to change the
resistors. Try doing the experiment with two different resistors.
You’ll find the same is true: the overall resistance always
equals the sum of the two separate resistances.
By experiment, we’ve just proved the law of series resistors.
And it doesn’t just stop at two resistors in series. Three, four,
five, in fact, any number of resistors may be in series — the
overall resistance is the sum of the individual ones. This can
be summarised mathematically as:
Try it yourself!
The next circuit
There is another way two or more resistors may be joined. Not
end-to-end as series joined resistors are, but joined at both
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