1. The problem statement, all variables and given/known data Find the electric force between the two spheres. Sphere r=b-a has a volumetric density of p=K, where K is a constant Sphere r=a has a volumetric density of p=θ*r 2. Relevant equations As you can see the sphere of radius 'a' doesn't have a uniform electric field because it varies with respect to 'θ' and 'r'. I need to know if the sphere of radius 'a' can be modeled as a point particle even if isn't uniformly charged? 3. The attempt at a solution The upper sphere can be modeled as a point particle because it is uniformly charged so I can obtain its charge which is Q = For the sphere centered at the origin I define an r vector between a point P inside the sphere of radius a in respect to the center of the upper sphere. Which after some arrangements leaves me with this expression for it's electric displacement field D = This field goes on the positive z direction. And this integral cannot be solved analytically as far as I know. Which is why I want to know if that sphere can be modeled as a point particle so I can just multiply the charges of each sphere?