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Day 8: Strength of Field, Right Hand Rule
Goal: Bring together information about direction and strength
to achieve a vector representation. Develop Cross-Product Formalism.
The big question that is before us is how to quantify the observations we
have made. As alluded to in the beginning of this unit, the magnetic field
is a vector quantity. As we have seen explicitly, the magnetic field has a
direction which tends to curve. That is, magnetic field lines cannot be
expected to be straight lines.
Further, the magnetic field lines seem to circle around and reconnect to
themselves. That is, they form closed loops. This can be established by
cutting a magnet into smaller and smaller pieces. Each piece will be have
opposite poles, and the opposite poles always go next to each other if the
pieces are returned to the original arrangement in the "uncut' magnet. By
an argument of extension to the limit of cutting the magnets into infinitely
small pieces, combined with never seeing like poles attract, we can reach
the 'accepted' conclusion that the magnetic fields lines are closed circles.
Finally, we seem to see that lines of current produce magnetic fields but
that the fields are never parallel to nor completely in the plane of the current.
Ask the students to form the simplest possible rule they can which allows
them to predict the shape of a magnetic field if they are told a long straight
current exists. Ask them to apply the rule to a circular current to test their model.
Discuss the right hand rule for finding the field direction for a given
current flow along a particular line.
Lesson Development/Writing: Ed Eckel
Web Design: Theresa Valentine
Last Updated: 8/11/2000
Above is background material for archival reference only.