PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 14)

10
Motor Accessory 012-06247A
¨
wire connected to the +
terminal of the power
supply
Figure 4. Determining the Direction of the Magnetic Field of the Coil Using the
Right-Hand Rule
When you wrap
your fingers in
the direction of
the flow of the
electric current,
your thumb
points towards
the north pole of
the magnetic
field.
+
+
Draw arrows indicating the direction
of current flow.
Indicate which pole: north (N) or south
(S). N
➤ 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, for more than a
century there was no way to resolve the issue. 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 gasses, current consists of electrons traveling in
one direction while positive ions move simultaneously in the opposite direction. In
solutions, current consists of oppositely charged ions traveling in opposing directions.
And in certain semiconductors, it is most useful to think of positive “holes” as being the
charge carriers.
Considering this complexity, scientists have found it most useful to continue the conven-
tion begun by Franklin: the “direction” of current is from positive to negative.