Figure shows a uniformly charged hemisphere of radius R. It has a volume charge density ρ. If the electric field at a point 2R, above its center is E, then what is the electric field at the point 2R below its center?

Let us complete the sphere. Electric field due to lower part at A is equal to electric field due to upper part at B = E (given) Electric field due to lower part at B = electric field due to full sphere − electric field due to upper part =kQ(2R)2−E=14πε0ρ(4/3)πR34R2−E=ρR12ε0−E