For Q > 0,
the work done against the repulsive force on the
test charge is positive Since work done is
independent of the path, we choose a convenient
path – along the radial direction from infinity to
the point P At some intermediate point P¢ on the path, the
electrostatic force on a unit positive charge is
2
0
1 ˆ
4
'
Q
εr
×
′
π
r
(2 5)
where ˆ′r is the unit vector along OP¢