如图所示，两根相距为l的平行直导轨ab、cd、b、d间连有一固定电_爱下问搜题

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问题选择题

如图所示，两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R，导轨电阻可忽略不计；MN为放在ab和cd上的一导体杆，与ab垂直，其电阻也为R；整个装置处于匀强磁场中，磁感应强度的大小为B，磁场方向垂直于导轨所在平面（指向图中纸面内）；现对MN施力使它沿导轨方向以速度v（如图）做匀速运动；令U表示MN两端电压的大小，则（　　）

A．U=vBl，流过固定电阻R的感应电流由b到d

B．U=vBl，流过固定电阻R的感应电流由d到b

C．U=vBl，流过固定电阻R的感应电流由b到d

D．U=vBl，流过固定电阻R的感应电流由d到b

答案

答案：A

完形填空

A young man was getting ready to graduate from college. For many months he had   16      a beautiful sports car in a dealer’s showroom, and knowing his father could well   17  it, he told him that was all he wanted.
On the morning of his graduation day his father called him into his own study and told him how   18  he was to have such a fine son. He handed his son a beautiful gift box.   19  but slightly disappointed（失望）, the young man opened the box and found a lovely book.   20 , he raised his voice at his father and said, “With all your money you give me a book?” and rushed out of the house,   21 the book in the study.
He did not contact his father for a whole year until one day he saw in the street an old man who looked like his father. He   22  he had to go back home and see his father.
When he arrived at his father’s house, he was told that his father had been in hospital for a week. The moment he was about to leave for the hospital, he saw on the desk the   23  new book , just as he had left it one year ago. He opened it and began to turn the pages. Suddenly, a car key   24      from an envelope（信封）in the book. It had a tag（标签）with the dealer’s name, the same dealer who had the sports car. On the tag was the   25  of his graduation, and the words “ PAID IN FULL”.

B．comfortable

填空题

热导池检测器可用的载气有（）