4. An annulus is a thin circular disk with a hole in it (or you can think of it as a ring with nonzero thickness). Here we will consider a charged annulus: charge is uniformly distributed between an inner radius R, and an outer radius R2. a) Determine the electric field a distance z above the center of the annulus. Do this two ways: . First, do this directly/explicitly using integration ( E = ffe ). This calculation should be very similar to what we did (or will do) for a full disk of charge. . Second, do this using superposition: treat the annulus as the superposition of two disks. For each disk, we know its electric field already, so you can just add them together. b) Show that your answer to part a) looks like a point charge in the limit that z > > R2. Express the electric field in terms of the total charge @ contained in the annulus