问题 选择题

由法拉第电磁感应定律知(设回路的总电阻一定)(  )

A.穿过闭合回路的磁通量达最大时,回路中的感应电流达最大

B.穿过闭合回路的磁通量为0时,回路中的感应电流一定为0

C.穿过闭合回路的磁通量变化量越大时,回路中的感应电流越大

D.穿过闭合回路的磁通量变化越快,回路中的感应电流越大

答案

由法拉第电磁感应定律E=n

△∅
△t
,可知感应电动势E与磁通量的变化率成正比,即感应电动势取决于磁通量的变化快慢,与其他因素没有直接关系,而感应电动势越大,闭合电路的感应电流则越大;故ABC错误,D正确.

故选:D.

阅读理解

阅读理解。

     Johnny Kelley is 86 years old. He has just run the last  eleven  kilometers of the  Boston Marathon. It

took  him  one  hour  and  fifteen  minutes to run the  eleven  kilometers. After his running, he went to the

hospital center. The nurse was surprised and pleased to see that his blood pressure was 139 over 84.

She told him that his blood pressure was very good. Then she said, "I wish mine were good like yours."

    Johnny Kelley is known as the great-grandfather of the Boston Marathon. He ran all the 42 kilometers

of the marathon 61 times. This year was the second time that he  has  cut  back  and  run  only  part of it.

Kelley holds the record for running more Boston Marathons than anyone else.

     Thousands  of  people  cry "Come on" to  him  as he runs. Today  an 11-year-old  boy called put to

Kelley, "Hey, Mr Kelley. You  are  great  man." Kelley  smiles  and  thanks  people  as he runs. "It's a

wonderful." He said, "People come out to shake my hand. I am welcomed by thousands of people. I

think a lot of them thought I ran the whole race. And maybe they congratulate because they know me

after all there years and they don't know the other runners."

1. Kelley is known as the great-grandfather of the Boston Marathon because _____.

A. he is eighty-six years old

B. he ran all the 42 kilometers of the Boston Marathon that day

C. he was old and ran all the 42 kilometers of the Boston Marathon 61 times

D. his grandson is the best runner of the Boston Marathon

2. When Kelley said it was wonderful, he meant that _____.

A. he was welcome by thousands of people

B. his blood pressure was so good

C. he was able to run the whole Marathon race

D. he got to the hospital center safely

3. Kelley keeps the record _____.

A. for living to a great age

B. for running the fastest

C. for taking one hour and 15 minutes to run the 11 kilometers

D. for running the most Boston Marathons

4. Kelley went to the hospital center after the race _____.

A. to tell the nurse the good news

B. to have a good rest

C. to thank people who cried "come on" to him

D. to see if his blood pressure was good

单项选择题