A large planar, thin insulating sheet is placed parallel to the horizontal and given a uniform positive charge density ${\text{σ=2×10}}^{\text{-4}}{\text{c/m}}^{\text{2}}\text{.}$ A small dipole of dipole moment $\left|\overrightarrow{\mathrm{p}}\right|\text{=}\left({\text{5×10}}^{\text{-7}}\right)\text{cm}$ is fixed above the sheet such that the dipole moment vector points in the vertically upward direction. The work done in slowly rotating the dipole such that its dipole moment vector now points in the vertically downward direction is ______ J. [Ignore gravity, take ${\text{ε}}_{\text{0}}\text{=}\frac{\text{80}}{\text{8}}{\text{×10}}^{\text{-12}}{\text{C}}^{\text{2}}{\text{/Nm}}^{\text{2}}$ ]