21变压器的电压比为3:1,若一次电流的有效值为3A,则二次电流的有效值为 ( )。
A.27A
B.9A
C.1A
D.0A
开始考试练习点击查看答案22有一信号源,内阻为60Ω,为使负载获得最大功率,在电源与负载之间接匹配变压器,该变压器的变比为2:1,则负载阻抗应为 ( )。
A.30Ω
B.20Ω
C.15Ω
D.10Ω
开始考试练习点击查看答案23提高功率因数前后,负载的( )不变。
A.![1591692532199530.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692532199530.jpg)
B.![1591692532852457.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692532852457.jpg)
C.![1591692532796836.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692532796836.jpg)
D.A、B、C都对
开始考试练习点击查看答案24电路如图6所示,8Ω电阻可获得最大功率时的变比n为( )。
A.10
B.100
C.0.1
D.0.01![1591692532846386.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692532846386.jpg)
开始考试练习点击查看答案25电路如图7所示,电路中电压源10∠0°V为有效值相量,则ab 端钮右侧电路所吸收的平均功率为( )。
A.
W
B.10W
C.3W
D.5W ![1591692532395548.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692532395548.jpg)
开始考试练习点击查看答案26电路如图8所示,正弦电源的频率
![1591692532141326.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692532141326.jpg)
,电路谐振时,
![1591692532742774.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692532742774.jpg)
( )。
A.10
B.1
C.100
D.1000![1591692533510744.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533510744.jpg)
开始考试练习点击查看答案27下列传输参数矩阵中,( )是互易、对称二端口网络。
A.![1591692533474723.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533474723.jpg)
B.![1591692533462125.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533462125.jpg)
C.![1591692533132133.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533132133.jpg)
D.![1591692533849725.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533849725.jpg)
开始考试练习点击查看答案28图9所示电路,
![1591692533554520.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533554520.jpg)
开关合上,电路中的时间常数
![1591692533616283.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533616283.jpg)
( )。
A.0.5 s
B.![1591692533643543.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533643543.jpg)
C.0.6 s
D.0.4 s![1591692533431057.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533431057.jpg)
开始考试练习点击查看答案29耦合电感线圈的初级自感和次级电感分别为3 H和7 H,则线圈的互感至多为( )
A.21 H
B.4.58 H
C.7 H
D.3 H
开始考试练习点击查看答案30图10所示正弦交流电路中,负载
![1591692533564938.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533564938.jpg)
![1591692533516827.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533516827.jpg)
获得最大功率时,
![1591692533819092.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692533819092.jpg)
应为( )。
A.
B.![1591692534877999.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692534877999.jpg)
C.
D.![1591692534383729.jpg](https://www.changlipeixun.com/d/tiku/ueditor/image/20200609/1591692534383729.jpg)
开始考试练习点击查看答案