Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

RE: How many volts?



Just in case anyone is still interested in the "How many volts?" problem,
here is one more approach that I understand may be just a bit different from
those already submitted:

Assume that the plates are horizontal, with plate 1 on top; that e represents
epsilon-nought; and that the charges on the plates are distributed uniformly
in the horizontal directions. Then the field between the plates and also
just above the top plate due to the charge Q1 alone is (Q1/A)/(2e). (It
seems to me that this doesn't depend on how the charge Q1 is distributed
between the upper and lower surfaces of the top plate.) Similarly, the field
between the plates and also just below the bottom plate due to the charge on
the bottom plate alone is (Q2/A)/(2e). (I mean these are the magnitudes of
the fields, taking Q1 & Q2 as absolute values.) Since between the
plates these fields point in the same direction, the resulting value there is
(Q1+Q2)/(2eA), which is then multiplied by the plate separation to get the
potential difference. Using the specified values gives:

(10nC+100nC)(.01m)/(1m^2)/(.00885nC^2/Nm^2)/2 = 62V


Fred Lemmerhirt
FredL@wccb.wcc.cc.il.us