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听录音，在正确的图片下面画“√”。 ( ) 1. A. B. ( ) 2. A. B. ( ) 3. A. B. ( ) 4. A. B.
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【简答题】一台三相同步电动机的数据如下：额定功率P N =2000kW，额定电压U N =3000V(星形联结)，额定功率因数cosφ N =0.9(超前)，额定效率η N =80%，同步电抗X s =1.5Ω，忽略定子电阻。当电动机的电流为额定值，cosφ=1时，励磁电流为5A。如功率改变，电流变为0.9I N ，cosφ=0.8(超前)，求此时的励磁电流(设空载特性为一直线)。
【单选题】Consider Figure 5.3. Assume that Swedish import companies behave as competitive buyers while foreign export companies behave as a monopoly seller. Compared to free trade, Sweden's import quota results...
A.
Gains totaling $3.20
B.
Gains totaling $4.80
C.
Losses totaling $3.20
D.
Losses totaling $4.80
【单选题】Monopoly results in a welfare loss because:
A.
marginal revenue does not equal marginal cost.
B.
the monopolist restricts output below the socially efficient level.
C.
average variable cost is not minimized.
D.
total cost is not minimized.
【单选题】Consider Figure 5.3. Assume that Swedish import companies behave as a monopoly buyer while foreign export companies behave as competitive sellers. Compared to free trade, Sweden's import quota results...
A.
Gains totaling $1.60
B.
Gains totaling $3.20
C.
Losses totaling $1.60
D.
Losses totaling $3.20
【简答题】1)改变励磁电流时,同步电动机的定子电流发生什么变化?对电网有什么影响?
【简答题】一台三相同步电动机的数据如下：额定功率PN=2000 kW，额定电压UN=3000 V(星形连接)，额定功率因数cosφN=0．9(超前)，额定效率ηN=80％，同步电抗Xt=1.5Ω，忽略定子电阻。当电动机的电流为额定值，cosφ=1时，励磁电流为5 A。如功率改变，电流变为0．9INcosφ=0．8(超前)，求此时的励磁电流(设空载特性为一直线)。
【单选题】In a monopolistically competitive industry, the competitive element results from ____ and the monopoly element results from ____.
A.
product differentiation; substantial barriers to entry.
B.
a large number of firms and free entry; product differentiation.
C.
advertising; product differentiation.
D.
product differentiation; the small number of large producers.
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