题干

如图所示是酒精浓度检测仪及其原理图,它实际上是由一节干电池(电压不变),一个气敏电阻R2(相当于阻值随酒精气体浓度变化的变阻器,酒精浓度越大阻值越小)与定值电阻R1及一个电压表组成.驾驶员呼出的酒精气体浓度越大,则(  )

 

A:气敏电阻R2的阻值越大,电压表的示数越大

B:通过电阻R2的电流越小,电压表的示数越大

C:通过电阻R1的电流越大,电阻R2两端电压越小

D:气敏电阻R2的阻值越大,通过R1的电流越大

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答案(点此获取答案解析)

C

同类题1

    One day, Susie was unhappy when she came home fromschool. “What's the matter, my dear?” asked her mother, drawing her to her sideand smiling.

   “All our class must hand in compositions tomorrow. We must write 12 linesat least. But I can never write one. I'll have to go to school without acomposition, for I won't copy one from a book, or ask you or papa to write onefor me.”

    “That's right,” said her mother. “You'll be happier with a poorcomposition, if it's your own, than with a fine one written by somebody else.But cheer up. Run into the garden and play. I'll call you in half an hour.Don't think about your composition now. Just have a good time.”

It seemed just a few minutes to Susie before she heard her mother calling her. She wentinto the house immediately — her hands full of sweet flowers, and her face redwith exercise.

Then her mother asked her to sit by the window with a nice piece ofpaper and a pencil, and write something about what she could see. “Never mindyour composition; do this to please me, and we'll talk about that later.”

    Although Susie thought her mother's request was strange, she knew shealways had a good reason for everything she did. So she did as her motherrequested.

    As she looked out, she first saw the western sky and some bright, sunsetclouds. “Oh, mother, what a sunset!”

“Don't talk. Just write.”

The pencil began moving rapidly across the paper. She wrote about the sunsetclouds, the look of the distant hills, the streets, the river, the garden withits flowers, and the birds flying past the window. She forgot all about theterrible composition!

    Just as she had reached the bottom of the page, hermother came in and said with a smile, “Well, Susie, how does that compositioncome on?”

   “Composition! You told me not to think about it, and I've never thoughtof it once. I've had such a nice time writing about what I could see from thewindow.”

    Mrs. Smith took the paper and read what Susie had written. She said,“There, Susie, that's a very nice composition,really.”

   “A composition! Is that a composition?”Susie asked in surprise.

   “Yes, my dear, and a very good one, too, if we find a title for it,”replied her mother. Then she added, “I'm sure it will please your teacher, asit does me. You see, it's easy enough to write a composition if you have anything interesting to write about.”