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MERLOT II


    

Peer Review


Electric & Magnetic Interactions: The Movies

 

Ratings

Overall Rating:

4 stars
Content Quality: 4 stars
Effectiveness: 4 stars
Ease of Use: 4 stars
Reviewed: Jul 22, 2002 by Physics
Overview: 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:

  1. Electric Fields

    1. Positive point charge: radial field is visualized as a function of
      distance.
    2. Negative point charge: similar to above.
    3. Dipole: field is visualized from a variety of angles.
    4. Dipole expanding and shrinking: field is visualized as the dipole
      separation is varied.
    5. Charged disk: field away from and close to the edges.
    6. Charged disk along midline: similar to above, but in a single plane.

  2. Magnetic Fields

    1. Moving proton: azimuthal field due to a moving charge, v << c.
    2. Right hand rule is illustrated.
    3. Long wire: azimuthal field is illustrated.
    4. Right hand rule for electron current: illustrated for flowing electrons.
    5. Right hand rule for conventional current: positive charge carriers.
    6. Compass above or below a wire: frame-by-frame explaining how the Earth's
      field will affect observation.

  3. Electromagnetic Radiation

    1. Electric field for an accelerated point charge.
    2. Electromagnetic radiation for an accelerated charge: radiated field for a
      brief acceleration.
    3. Electromagnetic Wave: E and B fields for a plane wave.
Learning Goals: 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: QuickTime movies
Recommended Uses: Tutorial, illustrations for course web pages and on-line homework.
Technical Requirements: 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

Content Quality

Rating: 4 stars
Strengths: 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.
Concerns: 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

Rating: 4 stars
Strengths: Both reviewers found these illustrations to be improvements over static textbook images.
Concerns:

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.


Ease of Use for Both Students and Faculty

Rating: 4 stars
Strengths: The clips are easy to use.
Concerns: None, other than file size.