Math. 311 Fall 1998
HOMEWORK SUMMARY REPORT
Week number:11
Problem number:7.4.2
Number of papers received:3
Reviewing committee (Greek letter): alpha
List all participating members:Dana Cloud, Mary Gregg
Author[s] of paper[s] chosen for publication: [Juan Juarez]
Comments:Dana and I were at a disagreement as to which paper was
correct. I believe the top and bottom of the integral cancel each other.
It is for this reason that we did not chose a paper for publication. Only
one paper gave any kind of explanation(Chris Clearman).
INSTRUCTOR'S COMMENT: The problem is that none of the papers (which are
all essentially correct) specified clearly that the electric field needs
to be evaluated ON THE SURFACE IN QUESTION (for instance, z = 7.5 on the
top). In skeletal notation, it looks like the top and bottom integrals
cancel, but there is no reason why the electric field at the top must be
equal to that at the bottom, so they don't cancel.
We chose Juan's paper over Chris's because Chris didn't say exactly
what he meant -- for instance, saying that E_r is the component of the
field "normal to the r axis", which should have been "normal to the
surface of constant r" or "parallel to the r axis" (if that means the
direction in which r is increasing as one moves through the point in
question).