6. (1 pt) A non-conducting annulus of radius 0.1m is centered at the origin x=y=0. The top half of the annulus (in black in the image below) is uniformly charged at 10'5 C/m2. The bottom half of the annulus (in grey in the image below) is also uniformly charged, with a density to be determined: a. What must be the charge density in the bottom half of the annulus for the electric field at the origin to be zero? b.What must be the charge density in the bottom half of the annulus for the electrical potential at the origin to be zero