题干

如图所示,平行导轨间距为d,一端跨接一个电阻R,匀强磁场的磁感应强度为B,方向垂直于平行金属导轨所在平面.一根金属棒与导轨成θ角放置,金属棒与导轨的电阻均不计.当金属棒沿垂直于棒的方向以恒定的速度v在金属导轨上滑行时,通过电阻R的电流是                                                                (  )

A:

B:

C:

D:

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D

同类题1

阅读下面文言文,完成小题

司空图

    司空图,字表圣,河中虞乡人。父舆,有风干。图,咸通末擢进士,礼部侍郎王凝特所奖待,俄而凝坐法贬商州,图感知己,往从之。凝起拜宣歙观察使,乃辟置幕府。召为殿中侍御史,不忍去凝府,台劾,左迁光禄寺主簿,分司东都。卢携以故宰相居洛嘉图节常与游。携还朝,过陕虢,属于观察使卢渥曰:“司空御史,高士也。”渥即表为僚佐。会携复执政,召拜礼部员外郎,寻迁郎中。

    黄巢陷长安,将奔,不得前。图弟有奴段章者,陷贼,执图手曰:“我所主张将军喜下士,可往见之,无虚死沟中。”图不肯往,章泣下。遂奔咸阳,间关至河中。僖宗次风翔,即行在拜知制诰,迁中书舍人。后狩宝鸡,不获从,又还河中。龙纪初,复拜旧官,以疾解。景福中,拜谏议大夫,不赴。后再以户部侍郎召,身谢阙下,数日即引去。

    图本居中修山王官谷,有先人田,遂隐不出。作亭观素室,悉图唐兴节士文人。名亭曰休休,作文以见志曰:“休、美也,既休而美具。故量才,一宜休;揣分,二宜休;耄而聩,三宜休;又少也惰,长也率,老也迂,三者非济时用,则又宜休。”因自目为耐辱居士。其言诡激不常,以免当时祸灾云。

    每岁时,祠祷鼓舞,图与闾里耆老相乐。王重荣父子雅重之,数馈遗,弗受。尝为作碑,赠绢数千,图置虞乡市,人得取之,一日尽。时寇盗所过残暴,独不入王官谷,士人依以避难。

朱全忠已篡,召为礼部尚书,不起。哀帝弑,图闻,不食而卒,年七十二。

(《新唐书•列传——九》有改动)

【注】卢携:(824年~880年),唐,字子升,范阳(今河北涿县)人。

同类题2

      Once there was a little girl who lived in a small, very simple, poor house on a hill. From there she could see across the valley to a wonderful house high on the hill on the other side. This house had golden windows, so golden and shining that the little girl would dream of how magic it would be to grow up and live in a house with golden windows instead of an ordinary house like hers. She wanted to live in such a golden house and dreamed all day about how wonderful and exciting it must feel to live there.
       When she got to an age and got enough skill and sensibility to go outside, she asked her mother if she could go for a ride outside the gate and down the lane. After pleading with her, her mother finally allowed her to go, insisting that she should keep close to the house and not wander too far. The day was beautiful and the little girl knew exactly where she was heading! Down the lane and across the valley, she got to the gate of the golden house across on the other hill.
       As she arrived, she focused on the path that led to the house and then on the house itself. She was so disappointed as she realized all the windows were ordinary and rather dirty, reflecting(反映出) nothing other than the sad neglect of the house that was derelict(废弃的).
So sad she didn't go any further and turned, and heart broken. As she glanced up she saw a sight to amaze her. There across the way on her side of the valley was a little house and its windows glistened golden as the sun shone on her little home.
      She realized that she had been living in her golden house and all the love and care she found there was what made her home the “golden house”. Everything she dreamed was right there in front of her nose!