大学MOOC Electrotechnics Ⅰ (Electrical Technology)(Dalian University of Technology)1458252167 最新慕课完整章节测试答案

Quiz

1、单选题：
​The silicon steel sheet used in transformer core is material (        ).​
选项：
A:
B:
C:
D:
答案: 【 】

Test for Chapter Five

1、单选题：

​Two identical AC iron core-windings are powered by two voltage sources. The voltages of the two power sources are the same while the frequencies are different ( f1 > f2 ), then which following description is right about 1  (           ) 2 .

​

​

​选项：
A:  < 
B: >
C: =
D: not sure
答案: 【  < 】

2、单选题：

‌For DC core coil, when the number of turns N of the coil is doubled, then the magnetic flux will （   ）.

‌

‌

‌

‌

‌选项：
A: increase
B: decrease
C: remain unchanged 
D: not sure
答案: 【 increase】

3、单选题：

‌For an AC core coil, when the core cross-sectional area A is doubled, the magnetic flux will (      ).

‍

‌

‍

‌

‍选项：
A: increase
B: decrease 
C: remain unchanged
D: not sure
答案: 【 remain unchanged】

4、单选题：
‍A DC electromagnet with rated voltage of 100V is connected to an AC power supply with voltage of 100V. Coil current I will (     ). ‎‍‎
选项：
A: increase
B: decrease
C: remain unchanged
D: not sure
答案: 【 decrease】

5、单选题：

‎A DC electromagnet with rated voltage of 100V is connected to an AC power supply with voltage of 100V. Magnetic flux    through the coil will (       ). 

​

‎

​选项：
A: increase
B: decrease
C: remain unchanged
D: not sure
答案: 【 decrease】

6、单选题：
‌The relationship between copper loss of a transformer is(       ).‏
选项：
A: proportional to load current squared 
B: proportional to load current 
C: inversely proportional to current
D: independent of load
答案: 【 proportional to load current squared 】

7、单选题：
‎The relationship between iron loss of a transformer and the  load (        ). ‌
选项：
A: increases with the increase of the load 
B: decreases with the increase of the load 
C: It has nothing to do with the load and remains unchanged
D: not sure
答案: 【 It has nothing to do with the load and remains unchanged】

8、单选题：

‍A load RL=8 is connected to a signal source through a transformer. The internal resistance R0 of the signal source is 800, and the number of turns of the primary winding N1 is 1000. If the load gets the maximum power through impedance matching, then the number of turns of the secondary winding N2 should be (      ).

‍

‍

‍选项：
A: 800
B: 100
C: 1000
D: 500
答案: 【 100】

9、单选题：
‏A single-phase transformer with rated capacity of SN=50kVA and the rated voltage of 10kV/230V. Given that the no-load current I0 is 3% of rated current and the output voltage at full load is 220V. Then the voltage regulation is (       ).‌‏‌
选项：
A: 0
B: 3%
C: 4.35%
D: 100%
答案: 【 4.35%】

10、单选题：
‏For capacitive load, when the current on the  secondary side increases, the output voltage on the secondary side  will (        ). ‏‏‏
选项：
A: increase
B: decrease
C: remain unchanged
D: not sure
答案: 【 increase】

11、填空题：

‎AC electromagnet, If U and f remain the same. 

​

‎The current i will            (increase/reduce/unchanged) when the air gap  is decreased.

​

‎

​答案: 【 reduce】

12、填空题：
‎A transformer is used for impedance matching. The resistance of the speaker should be increased from 4Ω to 100Ω in order to connect properly with the amplifier. How much is the impedance transformation ratio            . ‏
答案: 【 5】

13、填空题：

‎Two identical AC iron core-windings are powered by two voltage sources. The voltages of the two power sources are the same while the number of turns are different ( N1 > N2 ), then   1         2  .(<, >, =)

​

‎

​答案: 【 <】

14、填空题：
‍A 50 kV·A single-phase transformer which rated voltage is 6600 / 230 V.cosφ2=0.8. Given that the core loss is 600W, the copper loss is 1500W. U2=220 V(full-loading).‎‍Find the efficiency of the transformer (full-loading).                 %‎‎‍‎
答案: 【 (94,95)】

15、填空题：
‏A single-phase transformer with a capacity of 50kV×A and rated  voltage of 3300/220V. The transformer is operating at its rated capacity. If fluorescent lamps(40W, 220V) with power factor of 0.5 are used on the secondary side, how many lamps can be connected all together (ignore the loss of ballast).                    ‍
答案: 【 625】

Quiz

1、单选题：
‎In order to realize interlocking control, two AC contactors are used. Which of the following is right.(        )​‎​
选项：
A:
B:
C:
D:
答案: 【 】

Quiz

1、单选题：

​= 30 V, = 1.2 A, and the power factor is 0.257.The total apparent power in a balanced Y-connected load is (               ).

​选项：
A: 62.35VA
B: 47.52VA
C: 108VA
D: 36VA
答案: 【 62.35VA】

2、单选题：
‌ The average power in each phase of a balanced three-phase system is 1,200 W, and the total power is (      ).‎
选项：
A: 1200W
B: 3600W
C: 400W
D: 7200W
答案: 【 3600W】

3、单选题：
‍In a certain Y-connected balanced load, the line voltages are 380V and the impedances are 30+j40 Ω.  the total reactive power is (       ). ​‍​
选项：
A: 4.011kvar
B: 5.670kvar
C: 2.316kvar
D: 1.337kvar
答案: 【 2.316kvar】

Teat for Chapter Four

1、单选题：
‎ Two major parts of an ac generator are (        ). ‌
选项：
A: rotor and stator
B: rotor and stabilizer 
C: regulator and slip-ring
D: magnets and brushes 
答案: 【 rotor and stator】

2、单选题：
‏ The phase current produced by a certain 240 V, Y-connected generator is 12 A. The corresponding line current is (        ).‏
选项：
A: 36 A
B: 4.0A
C: 12A
D: 6.0
答案: 【 12A】

3、单选题：
‌  A certain ∆-connected generator produces phase voltages of 30 V. The magnitude of the line voltages are (      ). ‍
选项：
A: 10V
B: 30V
C: 90V
D: none of these 
答案: 【 30V】

4、单选题：
‌ If the source phase voltages of a ∆-Y system （A ∆-connected source driving a Y-connected load）are 220 V, the magnitude of the load phase voltages is  （      ）.‍
选项：
A: 220V
B: 380V
C: 127V
D: 73,3
答案: 【 127V】

5、单选题：

‍ A balanced, three-phase, -connected load has a line voltage of 200V and a total power consumption of 4800W at a lagging power factor of 0.8. The phase current of each load  is (       ).

​选项：
A: 10A
B: 17.31A
C: 14.14A
D: None of these
答案: 【 10A】

6、判断题：
‏Voltages across the generator windings are called line voltages‍
选项：
A: 正确
B: 错误
答案: 【 错误】

7、判断题：
‌A Y-connected system can have either three or four wires.‌
选项：
A: 正确
B: 错误
答案: 【 正确】

8、判断题：
‎In a ∆-connected generator the line currents and the phase currents are equal. ‎
选项：
A: 正确
B: 错误
答案: 【 错误】

9、判断题：
‌ In a  balanced system the neutral  line can be removed. ​
选项：
A: 正确
B: 错误
答案: 【 正确】

10、判断题：
​In a certain ∆-connected balanced load, the line voltages are 250 V and the impedances are 50∠30° Ω. the total apparent power is 3.75kVA.‎
选项：
A: 正确
B: 错误
答案: 【 正确】

Quiz

1、单选题：

‌Find I by Thévenin's Theorem(           ).

‏

‌

‏

‌

‏选项：
A: 1A
B: 2A
C: 3A
D: 4A
答案: 【 1A】

Test for Chapter One

1、单选题：

‍In the circuit shown in the following Figure .When the resistance R2 increases, the current I will(        ).

‎

‍

‎选项：
A: increase
B: decrease
C: remain the same
D: not sure
答案: 【 increase】

2、单选题：

In the circuit shown in the following Figure ,the voltage between the A and B ,ＵAB is （ ）.

‌