Video Transcript
The picture shows the electrons and
atomic nuclei in a section of copper wire. The blue circles represent
electrons, and the red circles represent atomic nuclei. An electric potential difference is
set up between the left-hand end and the right-hand end of the wire. Which of the following statements
best describes what will happen in the wire? (A) The electrons will move toward
the center of the wire. (B) The electrons will begin to
move toward one end of the wire. (C) The electrons will move outside
of the wire. (D) Nothing will happen.
This question is asking about the
behavior of electrons in a copper wire when an electric potential difference is
present. Let’s recall that a copper wire is
conductive. This means that electrons are able
to move freely between atoms in a copper wire. Let’s also recall that if an
electric potential difference is set up between the two ends of the wire, this
results in an electric current in the wire. And now, let’s recall that an
electric current is a flow of electric charges in a single direction.
We see then that an electric
potential difference across the left- and right-hand ends of the wire will result in
the electrons in the wire all moving in a single direction. This means that option (D) must be
rejected, as it states that nothing will happen. And we know that something will
happen; an electric current will be produced, and the electrons will move in the
wire. The other options all say that the
electrons will move, but each option describes different electron motion
directions. We must determine which option
describes the motion of the electrons correctly.
Option (C) states that electrons
will move outside of the wire. Recall that since copper is a
conductor, electrons are able to move freely between atoms in a copper wire. Now, an electron cannot get outside
of the wire by moving between atoms that are in the wire. We must therefore reject option
(C).
Option (A) states that electrons
will move toward the center of the wire. For electrons to move toward the
center of the wire, some electrons must move toward the left, while other electrons
must move toward the right. If this happened, the electrons
could not all be moving in the same direction. We’ve seen though, that an electric
potential difference produces an electric current, which means the electrons are all
moving in a single direction. So, we should reject option
(A).
The correct answer is option
(B). The electrons will begin to move
toward one end of the wire when an electric potential difference is set up between
the ends of the wire.
