The electric field in a region is given by : $\mathrm{E}=\left(4\mathrm{axy}\sqrt{\mathrm{z}}\right)\hat{\mathrm{i}}+\left(2{\mathrm{a}}^2\sqrt{\mathrm{z}}\right)\hat{\mathrm{j}}+\left({\mathrm{ax}}^2\mathrm{y}/\sqrt{\mathrm{z}}\right)\hat{\mathrm{k}}$ where a is a positive constant. The equation of an equipotential surface will be of the form