A solid conducting sphere of radius is positively charged and surrounded by a negatively charged concentric spherical shell of radius . The charge on the inner sphere is + and the charge on the outer sphere is -, respectively.
The figure to the right shows a cutout cross section of the two concentric conducting spheres. Let represent the distance from the center of the spheres.
7a) What is the electric field (magnitude and direction) in the following regions of space:
i) At the center of inner sphere, at a radial distance =0,
ii) Between the two spheres, at a radial distance , where iii) Outside of both spheres, at a radial distance >?

7b) If the potential difference between the two spheres is ∆=/40 40, what is the capacitance of the two conducting spheres?