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Starting electronics
Note that current (and voltage) scales read in the opposite
direction to the resistance scale we used in the last chapter,
and they are linear. This makes them considerably easier to
use than resistance scales and they are also more accurate as
you can more easily judge a value if the pointer falls between
actual marks on the scale.
Voltages
When you measure voltages with your multi-meter the same
procedure should be followed, using the highest voltage
ranges first and stepping down as required. The voltages
you are measuring here are all direct voltages as they are
taken from a 9 V d.c. battery. So you needn’t bother using the
three highest d.c. voltage ranges on the multi-meter, as your
9 V battery can’t generate a high enough voltage to damage
the meter anyway. Also, don’t bother using the a.c. voltage
ranges as they’re — pretty obviously — for measuring only
alternating (that is, a.c.) voltages.
As an example you can build the circuit of Figure 3.9 up on
your breadboard, shown in Figure 3.11. What is the measured
voltage? It should be about 4.5 V.
Now measure the voltage across the other resistor — it’s
also about 4.5 V. Well, that figures, doesn’t it? There’s about
4.5 V across each resistor, so there is a total of 2 x 4.5 V that
is, 9 V across them both: the voltage of the battery. This has
demonstrated that resistors in series act as a voltage divider
or a potential divider, dividing up the total voltage applied
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