The first nine questions test general understanding; questions 10 to 18 are numerical problems based mainly on the equivalent circuit; questions 19 to 26 are discursive questions related to d.c. machines; and the remaining questions are more challenging, with an applications bias.

1. What is the primary (external) parameter that determines the speed of an unloaded d.c. motor?

2. What is the primary external factor that determines the steady-state running current of a d.c. motor, for any given armature voltage?

3. What determines the small current drawn by a d.c. motor when running without any applied mechanical load?

4. What determines how much the speed of a d.c. motor reduces when the load on its shaft is increased? Why do little motors slow down more than large ones?

5. What has to be done to reverse the direction of rotation of:

   1. a separately excited motor;

   2. a shunt motor;

   3. a series motor?

6. Most d.c. motors can produce much more than their continuous-lyrated torque. Why is it necessary to limit continuous torque?

7. What is the basic difference between a d.c. motor and a d.c. generator?

8. From the point of view of supply, an unloaded d.c. motor running light looks like a high resistance, but when running at full load it looks like a much lower resistance. Why is this?

9. Why do d.c. motors run faster when their field flux is reduced?

10. A separately excited d.c. motor runs from a 220 V supply and draws an armature current of 15 A. The armature resistance is 0.8V.