Make Electronics

Experiencing Electricity 35

Experiment 5: Let’s Make a Battery

BAckground

Positive and negative

If electricity is a flow of electrons, which have a negative
charge, why do people talk as if electricity flows from the
positive terminal to the negative terminal of a battery?

The answer lies in a fundamental embarrassment in the
history of research into electricity. For various reasons, when
Benjamin Franklin was trying to understand the nature of
electric current by studying phenomena such as lightning
during thunderstorms, he believed he observed a flow of
“electrical fluid” from positive to negative. He proposed this
concept in 1747.

In fact, Franklin had made an unfortunate error that
remained uncorrected until after physicist J. J. Thomson
announced his discovery of the electron in 1897, 150 years
later. Electricity actually flows from an area of greater nega-
tive charge, to some other location that is “less negative”—
that is, “more positive.” In other words, electricity is a flow
of negatively charged particles. In a battery, they originate
from the negative terminal and flow to the positive terminal.

You might think that when this fact was established, every-
one should have discarded Franklin’s idea of a flow from
positive to negative. But when an electron moves through a
wire, you can still think of an equal positive charge flowing
in the opposite direction. When the electron leaves home,
it takes a small negative charge with it; therefore, its home
becomes a bit more positive. When the electron arrives at
its destination, its negative charge makes the destination a
bit less positive. This is pretty much what would happen if
an imaginary positive particle traveled in the opposite direc-
tion. Moreover, all of the mathematics describing electrical
behavior are still valid if you apply them to the imaginary
flow of positive charges.

As a matter of tradition and convenience we still retain Ben
Franklin’s erroneous concept of flow from positive to nega-
tive, because it really makes no difference. In the symbols
that represent components such as diodes and transistors,
you will actually find arrows reminding you which way

these components should be placed—and the arrows all

point from positive to negative, even though that’s not the

way things really work at all! Ben Franklin would have been

surprised to learn that although most lightning strikes occur

when a negative charge in clouds discharges to neutralize

a positive charge on the ground, some forms of lightning

are actually a flow of electrons from the negatively charged

surface of the earth, up to a positive charge in the clouds.

That’s right: someone who is “struck by lightning” may be

hurt by emitting electrons rather than by receiving them, as

shown in Figure 1-75.

Figure 1-75. In some weather conditions, the flow of electrons

during a lightning strike can be from the ground, through your

feet, out of the top of your head, and up to the clouds. Benjamin

Franklin would have been surprised.