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: The sign of work



On Mon, 6 Mar 2000, Kirkpatrick, James wrote:

... the reason for the minus sign [in dV = -E*ds], really is the
fact that potential is defined to be zero at infinite distance from the
charge.

I think James may be confusing the sign in the gradient relationship with
the sign of the absolute potential near a negative point charge. The sign
in the gradient relationship between V and E has nothing directly to do
with the value of the absolute potential at any given place. Both are
arbitrary, and independently so. We choose to have a minus sign in the
gradient relationship simply because we want positive charges to be forced
toward lower potentials by electric fields. This choice is universally
accepted. It is also completely independent of our choices 1) for a
reference position and 2) for the value of V *at* the reference position,
choices which are far less universal.

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm