Page 79 - Electric Machinery Fundamentals

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1-7. How does the relative permeability of a ferromagnetic material vary with magneto-
motive force?
1-8. What is hysteresis? Explain hysteresis in tenns of magnetic domain theory.
1-9. What are eddy current losses? What can be done to minimize eddy current losses in
a core?
1- 10. Why are all cores exposed to ac flux variations laminated?
1-11. What is Faraday's Jaw?
1- 12. What conditions are necessary for a magnetic field to produce a force on a wire?
1-13. What conditions are necessary for a magnetic field to produce a voltage in a wire?
1- 14. Why is the linear machine a good example of the behavior observed in real dc
machines?
1- 15. The linear machine in Figure 1-19 is running at steady state. What would happen to
the bar if the voltage in the battery were increased? Explain in detail.
1- 16. Just how does a decrease in flux produce an increase in speed in a linear machine?
1-17. Will current be leading or lagging voltage in an inductive load? Will the reactive
power of the load be positive or negative?
1-18. What are real, reactive, and apparent power? What units are they measured in? How
are they related?
1-19. What is power factor?

PROBLEMS
1- 1. A motor's shaft is spinning at a speed of 1800 r/min. What is the shaft speed in ra-
dians per second?
2
1-2. A flywheel with a moment of inertia of 4 kg • m is initially at rest. If a torque of
6 N • m (counterclockwise) is suddenly applied to the flywheel, what will be the
speed of the flywheel after 5 s? Express that speed in both radians per second and
revolutions per minute.
1-3. A force of 10 N is applied to a cylinder of radius r = 0.15 m, as shown in Figure Pl-I.
The moment of inertia of this cylinder is J = 4 kg • m • What are the magnitude and
2
direction of the torque produced on the cylinder? What is the angular acceleration a.
of the cylinder?

r=O.lSm
J=4kg·m 2

'"
r=lON
FIGURE Pl-l
The cylinder of Problem 1-3.