A short cylinder, of radius a and length L, carries a "frozen-in" uniform polarization P, parallel to its axis. Find the bound charge, and sketch the electric field (i) for L >> a. (ii) for L << a, and (iii) for L m a. [This device is known as a bar electret; it is the electrical analog to a bar magnet. In practice, only very special materials--barium titanate is the most "familiar" example--will hold a permanent electric polarization. That's why you can't buy electrets at the toy store.]