  Dimensional analysis, superposition principle, and continuity of electric
potential are used to study electric potential of a uniformly charged square
sheet at its plane. It is shown that knowing the electric potential on the
diagonal and inside the square sheet is equivalent to knowing it everywhere on
the plane of square sheet. Behavior of electric potential near the center of
the square is obtained. Then exact solution for the electric potential at any
point on the plane of the square sheet is obtained. This result is used to
calculate the electric potential of a right triangular sheet on its plane which
can be used to find electric potential at any point on the plane of any
uniformly charged polygon sheet.
