题干

小灯泡通电后其电流I随所加电压U变化的图线如图所示,P为图线上一点,PN为图线在P点的切线,PQ为U轴的垂线,PM为I轴的垂线,则下列说法中正确的是(  )

A:对应P点,小灯泡的电阻为R= U1I2

B:对应P点,小灯泡的电阻为R= U1I2I1

C:对应P点,小灯泡的功率为图中三角形POQ所围面积大小

D:对应P点,小灯泡的功率为图中矩形PQOM所围面积大小

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答案(点此获取答案解析)

A,D

同类题1

阅读下面的文字,完成小题。

槐花

阿来

    突然袭来一股浓烈的花香。谢拉班在梦醒时突然感到过分的宁静,还闻到了稠重浓烈的花香。是槐花的香气。他关了灯,仰躺在床上。岗亭的顶尖就成了一只幽深的倒悬的杯子,里面斟满往事的气味。

    花香又一次袭来。谢拉班掀开楼顶口的盖板,下了楼梯。转过身子时,他发现了墙外河边的槐树。树和他就只隔着一条马路一扇铁栅门。目力所及,凡是被灰蒙蒙的灯光映射的地方都有巨大的寂静存在。而那些灯光照射不到的树林里、田野里、村庄里的夜晚似乎充满了声音,野兽走动,禽鸟梦呓,草木生长,夜风吹动……妻子死了,当派出所长的儿子看他孤独,为他办了农转非手续。这个以前远近闻名的猎手成了车场的守夜人。

    警车尖利的叫声划破了寂静。儿子他们又抓住小偷或者什么别的坏人了吗?谢拉班为那个小家伙担心了,虽然他知道小家伙不在城里。他曾听儿子说过:“叫小家伙不要再遇见我,他干的事够他蹲两年监狱。”

    躺在床上,闭上眼睛,那小家伙向他走来。那眉眼,那暴突的门牙都给人一种稚气的感觉。小家伙稚气未脱却故作老成,用一种突然有了钱,见了一点世界的大大咧咧的口气跟他说话:“嗨,老头……”谢拉班却偏偏对这么一个不懂礼貌的小家伙怀着父亲般的慈爱。他用哄孩子一样的声音说:“把车停好,停好。”停好车了,他又叮嘱他收好东西,关上车窗,上锁。每次都是等小家伙走远了,谢拉班才突然意识到:天哪,家乡话!老头已经很久不说家乡话了。除了家乡话,他只能讲几句和守车有关的不连贯的汉语。所以几乎失去了说话的机会。

    他刚进城时不住在这里,跟儿子和儿媳妇住在一起。儿媳妇说汉语,戴着眼镜,说话轻声细语。谢拉班尤其喜欢她那口整齐洁白的牙齿。儿媳妇给了他一间专门的房子。床低矮柔软。墙上挂着他舍不得卖掉的火枪,一对鹿角、几颗野猪獠牙和几片野鸡翎子。窗下有一张躺椅,上面铺着熊皮。儿媳妇经常让同事和上司来参观,这个老猎手的房间引起了他们的赞叹。谢拉班终于渐渐明白,那赞叹不是冲他来的,而是冲着儿媳妇,赞叹她对一个形貌古怪的藏族公公的孝敬而发的。最终的结果是她成了妇联的领导。那天家里摆了酒,还有好多的菜。吃完,儿媳妇用牙签拨弄牙缝,拨断了几根签子也没弄出点什么。她大张开嘴唇,这时,全部上牙就掉了下来。儿媳妇可爱的牙齿是假的!谢拉班对儿子说:“我受不了了。”

     “为什么?”“你老婆是假的,牙齿。是你打掉的吗?”儿子摇头。儿媳妇问丈夫:“你们说什么,你们用汉话谈吧。”“父亲不会。”“慢慢学嘛。”说完,她就端起那个装假牙的杯子进了另一间房子。谢拉班突然高声说:“我要回家!”于是他就成为车场的守夜人了。

    刚守夜的时候还没有这个专门的停车场。原先的车都停在一个僻静的十字街口。守夜人住在一幢六层楼房下平时不用的安全门洞里,门洞很小,刚好能放下一架床、一只火炉和他宽大的身子。后来,他把儿子为他架的床拆了,在地上铺上那张熊皮,听着火炉里的噼啪声和那好闻的松脂香气,在熊皮上安然入眠。

    小家伙每次都给他捎来东西:一捆引火的干树枝,点燃后熏除蚊虫和秽气的新鲜柏枝,糖果,甘蔗,鼻烟,甚至还带来过一摞连环画和一把玩具手枪。然后就和他告别,上街吃饭,打下点小注的台球。有一次,小家伙从车上抱出来大把洁白芬芳的槐花,他把槐花扔在熊皮上,小屋里立即充满了槐花的香气。他又从车上取下一小袋麦面,说:“做个馍馍吧,家乡的槐花馍馍吧。”谢拉班生火,烧水,和面,在面粉中掺进细碎的槐花瓣子。馍馍熟了。馍馍上纹路开阔,眉开眼笑,香气四溢。小屋里缭绕着甘甜的槐花香气。

    现在。在这个槐花初放、香气浓郁的夜半,谢拉班躺在床上,他好像又看到说家乡话的小家伙从车上下来时摹仿那些最老成的司机的姿态,听见他喊:“老头,嗨!”

    组成这个城市的建筑正从模糊的、似梦非梦的灯光下解脱出来,谢拉班就从床上起来。那天他花了很长时间把一些废钢条绑成了一架梯子,把梯子扛到槐树下,采摘了许多芬芳洁白的槐花。

(选自《阿坝阿来》,有改动)

同类题4

阅读理解

    In 1943, when I was 4, my parents moved from Coeur d'Alene, Idaho, to Fairbanks, Alaska, where adventure was never very far away.

    We arrived in the summer, just in time to enjoy the midnight sun. All that sunlight was fantastic for Mum's vegetable garden. Working in the garden at midnight tended to throw her timing off, so she didn't care much about my bedtime.

    Dad was a Railway Express agent and Mum was his clerk. That left me in a mess. I usually managed to find some trouble to get into. Once I had a little fire going in the dirt basement of a hotel. I had tried to light a barrel(桶) of paint but couldn't really get a good fire going. The smoke got pretty bad, though, and when I made my exit, a crowd and the police were there to greet me. The policemen took my matches and drove me home.

    Mum and Dad were occupied in the garden and Dad told the police to keep me, and they did! I had a tour of the prison before Mum rescued me. I hadn't turned 5 yet.

    As I entered kindergarten, the serious cold began to set in. Would it surprise you to know that I soon left part of my tongue on a metal handrail at school?

    As for Leonhard Seppala, famous as a dog sledder(驾雪橇者), I think I knew him well because I was taken for a ride with his white dog team one Sunday. At the time I didn't realize what a superstar he was, but I do remember the ride well. I was wrapped(包裹) heavily and well sheltered from the freezing and blowing weather.

    In 1950, we moved back to Coeur d'Alene, but we got one more Alaskan adventure when Leonhard invited us eight years later by paying a visit to Idaho to attend a gathering of former neighbors of Alaska.