The method of images may be applied to a sphere as well. In fact, the case of image charges in a plane is a special case of the case of images for a sphere. Referring to the figure, we wish to find the potential inside a grounded sphere of radius R, centered at the origin, due to a point charge inside the sphere at position p (For the opposite case, the potential outside a sphere due to a charge outside the sphere, the method is applied in a similar way). In the figure, this is represented by the green point. Let q be the point charge of this point. The image of this charge with respect to the grounded sphere is shown in red. It has a charge of q ′ = − qR / p and lies on a line connecting the center of the sphere and the inner charge at vector position ( R 2 / p 2 ) p . It can be seen that the potential at a point specified by radius vector r due to both charges alone is given by the sum of the potentials: