Introduction to Electric Current
To understand the nature of electric current and the conditions under which it exists.
is defined as the motion of electric charge through a
. Conductors are
materials that contain movable charged particles. In metals, the most commonly used conductors, such
charged particles are electrons. The more electrons that pass through a cross section of a conductor per
second, the greater the current. The conventional definition of current is
is the current in a conductor and
is the total charge passing through a cross section of
the conductor during the time interval
The motion of free electrons in metals not subjected to an electric field is
: Even though the
electrons move fairly rapidly, the net result of such motion is that
(i.e., equal numbers of
electrons pass through the cross section in opposite directions). However, when an electric field is
imposed, the electrons continue in their random motion, but in addition, they tend to move in the
direction of the force applied by the electric field.
In summary, the two conditions for electric current in a material are the presence of
in the material and the presence of an
Quantitatively, the motion of electrons under the influence of an electric field is described by the
, which tends to be much smaller than the speed of the random motion of the electrons. The
number of electrons passing through a cross section of a conductor depends on the drift speed (which, in
turn, is determined by both the microscopic structure of the material and the electric field) and the cross-
sectional area of the conductor.
In this problem, you will be offered several conceptual questions that will help you gain an
understanding of electric current in metals.
You are presented with several long cylinders made of different materials. Which of them are likely to
be good conductors of electric current?
Check all that apply.