问题 选择题

在探究“怎样产生感应电流”的实验中,蹄形磁体水平放置,如图所示。闭合开关,要使灵敏电流计的指针发生偏转,导体ab应

A.竖直向上运动

B.水平向右运动

C.保持静止不动

D.竖直向下运动

答案

答案:B

题目分析:产生感应电流的条件是闭合电路的一部分导体在磁场中切割磁感线,在图中ab竖直向上运动时,没有切割磁感线,因此没有电流产生,灵敏电流计的指针不发生偏转,选项A不符合题意;图中ab水平向右运动时,切割磁感线,因此产生感应电流,灵敏电流计的指针发生偏转,选项B符合题意;图中ab保持静止不动时,没有切割磁感线,因此没有电流产生,灵敏电流计的指针不发生偏转,选项C不符合题意;图中ab竖直向下运动时,没有切割磁感线,因此没有电流产生,灵敏电流计的指针不发生偏转,选项D不符合题意;答案选B.

单项选择题
单项选择题

It’s a typical Snoopy card: cheerful message, bright colors, though a little yellow and faded now. Though I’ve received fancier, more expensive cards over the years, this is the only one I’ve saved. One summer, it spoke volumes to me.
I received it during the first June I faced as a widow to raise two teenage daughters alone. In all the emotional confusion of this sudden single parent- hood, I was overwhelmed with, of all things, the simplest housework: leaky taps, oil’ changes, even barbecues (烧烤). Those had always been my husband’s jobs. I was embarrassed every time I hit my thumb with a hammer or couldn’t get the lawnmower (割草机) started. My uncertain at- tempts only fueled the fear inside me: How could I be both a father and mother to my girls Clearly, I lacked the tools and skills.
On this particular morning, my girls pushed me into the living room to see something. (I prayed it wasn’t another repair job). The "something" turned out to be an envelope and several wrapped bundles on the carpet. My puzzlement must have been plain as I gazed from the colorful packages to my daughters’ bright faces.
"Go ahead! Open them!" they urged. As I unwrapped the packages, I discovered a small barbecue grill (烧烤架) and all the necessary objects in- eluding a green kitchen glove with a frog pattern on it.
"But why" I asked.
"Happy Father’s Day!" they shouted together.
"Moms don’t get presents on Father’s Day," I protested.
"You forgot to open the card," Jane reminded. I pulled it from the envelope. There sat Snoopy, on top of his dog house, merrily wishing me a Happy Father’s Day. "Because," the girls said, "you’ve been a father and mother to us. Why shouldn’t you be remembered on Father’s Day"
As I fought back tears, I realized they were right. I wanted to be a "professional" dad, who had the latest tools and knew all the tricks of the trade. The girls only wanted a parent they could count on to be there, day after day, performing repeatedly the maintenance tasks of basic care and love.
The girls are grown now, and they still send me Father’s Day cards, but none of those cards means as much to me as that first one. Its simple message told me being a great parent didn’t require any special tools at all--just a willing worker.

What puzzled the mother when her daughters asked her to see something one morning

A. It was not another repair job this time.
B. Both of her daughters looked excited.
C. She got gifts at that time of the year.
D. The bundles on the floor were wrapped.