题干

如图,一理想变压器原、副线圈的匝数分别为n1、n2.原线圈通过一理想电流表A接正弦交流电源,一个二极管和阻值为R的负载电阻串联后接到副线圈的两端.假设该二极管的正向电阻为零,反向电阻为无穷大.用交流电压表测得a、b端和c、d端的电压分别为Uab和Ucd,则(   )

A:Uab:Ucd=n1:n2

B:增大负载电阻的阻值R,电流表的读数变小

C:负载电阻的阻值越小,cd间的电压Ucd越大

D:将二极管短路,电流表的读数加倍

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答案(点此获取答案解析)

B,D

同类题3

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    Bob was happy. He was at a new school, and the other students were friendly. “Hi, Bob!” they said. But some students said, “Hi, Peter!” Bob didn't understand. He asked another student, “Why do some students call me Peter?”
    “Oh, that's easy to answer,” the students said. “Peter was a student here last year. Now he goes to a different school. You look like Peter. Some students think that you're Peter.”
    Bob wanted to meet Peter. He got Peter's address from a student and went to Peter's house. Peter opened the door. Bob couldn't believe his eyes. He looked really like Peter! Bob and Peter had the same colour eyes and the same smile. They had the same black hair. They also had the same birthday. And they both were adopted(领养) by two different families.
    Bob and Peter found out that they were twin brothers. Soon after the boys were born, one family adopted Bob, and another family adopted Peter. Bob's family never knew about Peter, and Peter's family never knew about Bob.
    Bob and Peter's story was in the newspaper. There was a photo of Bob and Peter next to the story. A young man named John saw the photo in the newspaper. John couldn't believe his eyes. He looked really like Bob and Peter! He had the same colour eyes and the same smile. He had the same black hair. He had the same birthday. And he, too, was adopted by another family.
    Later John met Bob and Peter. When Bob and Peter saw John, they couldn't believe their eyes. John looked really like them! Why did John look really like Bob and Peter? You can guess. Bob and Peter are not twins. Bob, Peter and John are triplets(三胞胎).
    Choose the best answer: