We now have a grid of (x,y) values and are ready to calculate
the electric potential at these points.
In cell B2 enter the formula:
=0.2/SQRT(B$1^2+$A2^2)
Better yet just copy and paste it.
This is the formula for the electric potential due to
a particle with charge 2.224 X 10-11 C. The charge
doesn't necessarily correspond to anything real; it is simply
chosen so that kq=0.2 N m2/C.
Note that B$1 replaces x in the formula
kq/(x2+y2)1/2.
And $A2 replaces y in it.
All of the calculations we do here will be in the xy-plane,
i.e. the z coordinate is zero for all of them.
The placement of the dollar signs is crucial. Please
be careful.
When a formula is copied, the dollar sign tells Excel that
you do not want to change the part of the cell reference that
follows. Thus when the formula is copied, the B in
B$1 may change but the 1 won't (i.e. we are always referring
to a cell in the first row).
Similarly, when the formula is copied the 2 in $A2 may change
but the A won't (i.e. we are always referring to a cell in the
first column).
