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Starting electronics
But what is the right way round? And how do you tell the
difference? The answers are quite simple really; both given
by the fact that your multi-meter has two leads, one red, one
black. The colour coding is used to signify which lead to
connect to which point in a circuit. By convention, black is
taken to be the colour signifying a lower potential. Red, also
by convention, signifies a higher potential. So, the multi-meter
should be connected into the circuit with its red lead touching
the point of higher potential and the black lead touching the
point of lower potential. This is illustrated in Figure 3.6 with
symbols close to the multi-meter (+ for the red lead, – for the
black). In the circuit shown, the point of higher potential is
the side of the circuit to the positive terminal of the battery
(also marked +).
It doesn’t matter where in the circuit the multi-meter is placed,
the red lead must always connect to the point of higher potential.
Figure 3.7, for example, shows the multi-meter at a
different position, but the measurement is the same and the
multi-meter won’t be damaged as long as the red lead is connected
to the point of higher potential.
Negative vibes
Figures 3.1 to 3.7 all show current flowing from the positive
terminal of the battery to the negative terminal. Now we know
that current is made up of a flow of electrons so we might
assume that electrons also flow from positive to negative
battery terminals. We might — but we’d be wrong, because
electrons are actually negatively charged and therefore flow
from negative to positive battery terminals. But a negative
flow in one direction is exactly the same as a positive flow
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