A point charge q1 = +7e is fixed at the origin of a rectangular coordinate system, and a point charge q2 = -1 1e is fixed at x = 9.0 nm, y = 0. The locus of all points in the xy plane for which V = 0 (other than infinity) is a circle centered on the x axis, as shown in the figure. Find (in nm) (a) the location x of the center of the circle and (b) the radius R of the circle. (c) Is the xy cross section of the 5 V equipotential surface also a circle? V=0 R + - X Xc 91 92 (a) Number Units nm (b) Number i Units nm (c) no VMuch of the material making up Saturn's rings is in the form of tiny dust grains having radii on the order of 10'6 m. These grains are located in a region containing a dilute ionized gas, and they pick up excess electrons. As an approximation, suppose each grain is spherical, with radius R = 1.4 x 106 m. How many electrons would one grain have to pick up to have a potential of 31OV on its surface [taking V = D at innity)? (a) Figure (a) shows a nonconducting rod of length L = 8.20 cm and uniform linear charge density ) = +2.24 pC/m. Take V = 0 at infinity. What is V at point P at distance d = 5.80 cm along the rod's perpendicular bisector? (b) Figure (b) shows an identical rod except that one half is now negatively charged. Both halves have a linear charge density of magnitude 2.24 pC/m. With V = 0 at infinity, what is Vat P? FFF 1/2 - L/2 1/2- L/2 (a) (b) (a) Number Units V (b) Number i Units V