Short 3-D QuickTime movies of electric and magnetic fields in space, designed to assist physics students in visualizing fields. They depict spatial configurations of electric and magnetic fields that are frequently discussed in introductory physics courses. Specifically created to accompany the textbook href="http://cil.andrew.cmu.edu/mi.html">Matter & Interactions II: Electric & Magnetic Interactions, by Ruth Chabay and Bruce Sherwood (2002, John Wiley & Sons, NY). The individual files are as follows:
Positive point charge: radial field is visualized as a function of distance.
Negative point charge: similar to above.
Dipole: field is visualized from a variety of angles.
Dipole expanding and shrinking: field is visualized as the dipole separation is varied.
Charged disk: field away from and close to the edges.
Charged disk along midline: similar to above, but in a single plane.
Moving proton: azimuthal field due to a moving charge, v << c.
Right hand rule is illustrated.
Long wire: azimuthal field is illustrated.
Right hand rule for electron current: illustrated for flowing electrons.
Right hand rule for conventional current: positive charge carriers.
Compass above or below a wire: frame-by-frame explaining how the Earth's field will affect observation.
Electric field for an accelerated point charge.
Electromagnetic radiation for an accelerated charge: radiated field for a brief acceleration.
Electromagnetic Wave: E and B fields for a plane wave.
Conceptual understanding of electromagnetic fields.
Target Student Population:
Undergraduate, all levels
Prerequisite Knowledge or Skills:
Introduction to electricity and magnetism (High school or first year college course).
Type of Material:
Tutorial, illustrations for course web pages and on-line homework.
The user must have a QuickTime player installed. The video files are probably too large to be used without a server that can stream them.
Evaluation and Observation
One reviewer (reviewer 1) found these clips to have significant potential to improve instruction of abstract three-dimensional concepts covered in introductory classes. Another reviewer (reviewer 2) was less impressed, citing issues detailed below.
From reviewer 2:
The electric field vectors are drawn very big and there are relatively few of them. The diagrams look somewhat coarse. Since these are movies and the vectors do not have to be generated in real time by the computer, vector diagrams with somewhat higher resolution seem appropriate.
The charged disk clip illustrates edge effects correctly but does not convey that the field near the center of the disk are nearly constant as a function of distance. Also, in one of the movies just 3 rows of vectors are drawn, instead of extending the vector diagram over the whole viewing window.
This reviewer also had concerns that the clip showing a 2D view of an accelerated charge might oversimplify subtleties in ways that could be misleading. The text accompanying the movie states "At the boundary between these two regions the field is transverse (shown in red)", and the graphics seem to convey the same message. The radiation field is transverse, but the static and induction fields are not. At small distances these fields will be much larger in magnitude than the radiation field. It is not advisable to try to make field lines represent the static field and the radiation field at the same time.
Potential Effectiveness as a Teaching Tool
Both reviewers found these illustrations to be improvements over static textbook images.
Presenting the right-hand rule (or left-hand rule) and three slides as a movie does not convey much more information than presenting it as individual diagrams, but takes up much more bandwidth.