A flying airplane gains a negative charge on its surface due to friction with the air. Assuming these charges are uniformly spread on its wings, what is the electric field generated? Consider a small portion of the wing. The charge distribution remains unchanged under rotation about an axis perpendicular to it. Hence, the charge distribution has planar symmetry. Due to planar symmetry, the electric field is uniform and perpendicular to the surface on either side. A cylindrical Gaussian surface with its axis perpendicular to the plane and the flat ends equidistant from it is constructed. The electric flux over the curved surface is zero. The flux through the flat ends equals the electric field magnitude multiplied by the surface area. The total flux is, thus, twice the flux obtained from each flat surface. From Gauss's law, the charge enclosed is the product of the area of the flat surface and the surface charge density. Combining these, the electric field magnitude can be obtained.