(a) Describe "generating" in a dc machine. You may assume a dc field is produced by the stator. (b) Describe "motoring" in a dc machine. You may assume dc field is produced by the stator. (c) What is the key difficulty in trying to create a machine that is only supplied by dc sources? (d) What are the commutator and brushes used to achieve in a dc machine? (e) What is the machine constant in a dc machine? (f) What parameters define the induced armature voltage in the machine? Does this depend on if you are motoring or generating? (g) What is the equivalent circuit when generating and when motoring, assuming a separately excited machine? (h) Why are the values of the inductors in the dc machine circuits models unimportant? (i) What are the four ways to excite the stator field? (j) What electrical losses exist in the dc machine