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Assume that a stationary electron is a point of charge. What is the energy density u of its electric eld at radial distances (a) r = 3.90 mm, (b) r = 3.90 pm, (c) r = 3.90 nm, and (d) r = 3.90 pm? (e) What is u in the limit as r > 0? (Select option "1" if u > 0 or option "2" if u > 00.) In the figure how much charge is stored on the parallel-plate capacitors by the 18.0 V battery? One is filled with air, and the other is filled with a dielectric for which k = 2.90; both capacitors have a plate area of 7.10 x 10-3 m and a plate separation of 9.90 mm.The space between two concentric conducting spherical shells of radii b = 2.30 cm and a = 1.20 cm is lled with a substance of dielectric constant K = 13.3. A potential difference V = 42.0 V is applied across the inner and outer shells. Determine (a) the capacitance of the device, (b) the free charge q on the inner shell, and (c) the charge q induced along the surface of the inner shell. (3) Number a Units ' V' (b) Number a Units ' v' (c) Number n ' Units ' V