PASCO SE-8658A PERMANENT MAGNET MOTOR - Manual (Page 13)

9
012-07210A Permanent Magnet Motor
➤ Note: Here’s why the direction of conventional current is opposite to that of the
direction of electron flow: In the mid-eighteenth century, Benjamin Franklin suggested the
terms positive and negative, and conjectured that electrical current was the movement of
positive “fluid” from positive to negative regions. Although he understood that it was
equally possible that a negative fluid moves from negative to positive, there was no way to
resolve the issue for more than a century. By convention, scientists agreed to describe the
direction of current as being from positive to negative. Not until 1879 did Edwin H. Hall
show that in metals the current was a negative “fluid.” It remained for J. J. Thompson, R.
A. Millikan, and others to demonstrate the existence of electrons, which are the charge
carriers of this “fluid”. This might seem an argument for changing the convention. But
current doesn’t always travel in metals. In ionized gasses, current consists of electrons
traveling in one direction with positive ions moving simultaneously in the opposite
direction. In solutions, current consists of oppositely charged ions traveling in opposing
directions. And in certain semiconductors positive “holes” are the charge carriers.
Considering this complexity, scientists have found it most useful to continue the
convention begun by Franklin: the “direction” of current is from positive to negative.
wire connected to the +
terminal of the power
supply
Figure 1.4
Determining the Direction of the Magnetic Field of the Coil Using the Right-Hand Rule
+
+
Draw arrows indicating the direction
of current flow.
Indicate whether north (N) or south (S). N
When you wrap
your fingers in the
direction of the
current flow in a
coil, your thumb
points towards the
north pole of the
magnetic field.
direction of wire
wrapping on the coil