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Chapter 27
Magnetism
Introduction
• Our approach
– Review of E&M interaction ideas
– Magnetic fields & magnets (initial ideas)
– Magnetic field and currents (initial ideas)
– Force on a current in a B-field
– Force on a charge in a B-field
– Torque on a current loop in a B-field
– The Hall Effect
Electrical & Magnetic
interactions
• How have people understood the relation
between electrical and magnetic
interactions?
• Ancient views
• 19th Century: Classical E&M
• 20th Century: Special Relativity
• 20th Century: Quantum Field Theory
Magnets & Magnetic Field
• Magnetic poles
• Origin of pole names
• The Earth’s magnetic field
– Quick survey
– http://web.archive.org/web/20100625061648/
http://gsc.nrcan.gc.ca/geomag/nmp/daily_mvt
_nmp_e.php
Currents & Magnetic Fields
• Shape and direction of field caused by a
current (initial idea)
– Whiteboard example
• Use of the right hand rule to determine the
direction of the magnetic field
– Question posing
Force on a current in a B-field
• The force on a current element and
current
– Vector expression and picture
• The magnetic field as not a force field, as
was the electric field
– Why?
Force on a charge in B-field
• The force
– Vector expression and picture
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Relation to motion
Example: velocity selector
Example: electron behavior
Force from E and B fields
– What is it? And corresponding picture?
• Effect on motion
– What is it?
Torque on a current loop
in B-field
• The torque
– Why expected?
• Magnetic dipole moment
– Vector expression and picture
• The potential energy
– Vector expression and picture
• Review of key formulas
The Hall Effect
• Physical situation
– Describe the situation
• Underlying dynamics
– Provide an explanation
the end