Final answer:
The electric field just outside a uniformly charged spherical surface can be found using Coulomb's Law, where the charge is treated as if it were concentrated at the center of the sphere due to the symmetry.
Step-by-step explanation:
To find the electric field just outside the charged paint layer on a sphere, we can apply Gauss's Law. As the charge is spread uniformly on the surface of a spherical object, the electric field at any point just outside the surface can be calculated as if all the charge were concentrated at the center of the sphere. This results from the symmetry of the sphere and is a conclusion of Gauss's Law, which relates the flux through a closed surface to the enclosed charge.
In this case, with a plastic sphere of diameter 18.0 cm (which gives a radius of 9.0 cm or 0.09 m) and a charge of -49.0 μC (which is -49.0 x 10-6 C), the electric field E just outside the paint layer is given by the formula E = k|q|/r2, where k is Coulomb's constant (8.99 x 109 Nm2/C2), q is the charge, and r is the radius of the sphere.