题干

如图甲所示的电路中,电源电压恒定, R1 为定值电阻, R2 为滑动变阻器,闭合开关S后,滑动变阻器滑片P从一端向另一端滑动过程中,电压表 V2 电流表A示数变化情况如图乙所示,以下说法不正确的是(   )

A:R1 电阻为 5Ω

B:若滑动变阻器滑片P自b向a移动,电压表的 V1 示数不变,电路消耗的总功率变大

C:若滑动变阻器滑片P自b向a移动,电流表A的示数变大,电压表 V2 的示数与电流表A的示数之比变小

D:不管滑片P怎么移动,电压 V2 的示数变化量 △U2 与电流表A的示数变化量 △I 的比值不变

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答案(点此获取答案解析)

B

同类题2

阅读下文,完成小题。
                                                                                                                       快乐的木珠
                                                                                                                           魏振强
        ①下午带女儿去大院门口的街道上买西瓜。一溜子装瓜的车子排在那儿,女儿东瞅西瞅,最后在一个妇女的瓜摊前停了下来。她相中这个瓜摊,肯定是与妇女身边的小孩有关。那是个小男孩,3岁左右,头剃得光溜溜的,坐在那儿眯着眼似乎随时都会睡着。
       ②女儿蹲下来挑瓜时,男孩眯着的眼睛忽然打开了,他双手在地上一撑,弹起来,跑到女儿身边,伸出一双胖乎乎的小手,摩挲着她手腕上的木珠子。她的妈妈在边上吆喝他“别调皮”,可他没听进。女儿见他好玩,伸出另一只手,摸摸他葫芦一样的光头,他大概有点痒,咯咯咯地笑,笑出的一串涎水滴到了女儿的胳膊上。
        ③女儿把涎水在裤子上擦去,然后褪下了手腕上的珠子,递给小男孩,小家伙拿过珠子,往手上一套,舔了一口,笑着跑开了。他妈妈呵斥他回来,他仍然没听见,笑着在地上兜圈子,跑着跑着,被旁边的西瓜绊了一跤,嘴巴正好磕在另一只瓜上。女儿准备伸手去拉,他当是要抢回珠子,迅捷地爬了起来,煞有介事跑得远远的。
        ④女儿把瓜放在秤盘上,女人称好后,接过我付的钱,就去追小男孩,可这小子还在往前跑。女儿和我都在笑,一溜子卖瓜的人也在笑。女人终于追上他了,褪下珠子,往回跑,小男孩不干了,咧着嘴,跟在后面伤心欲绝地哭。
        ⑤女人笑着把珠子递给我女儿,但女儿没接。“送给他吧”,女儿说。女人一副慌张的样子,“不能要不能要。”边说边往我女儿手上塞。女儿红着脸,把双手背在身后,“不值钱的,给他吧。”小男孩此时已跑到跟前,见他妈妈正把珠子给别人,哭声更嘹亮了。女儿看着,不停地笑,然后从女人手里接过珠子,往小男孩手上套,他的哭声立马打往,脸上立刻堆满了笑容,鼻涕也笑成了小泡泡。
        ⑥我们离开时,女人执意要塞给我们另一个瓜,我们当然没要。傍晚时,我们去散步,那妇女正弯腰收摊子,小男孩一看到我们就跑开了。跑到远处,高举着套着珠子的手臂,立在那儿,笑着向我们炫耀,那样子就像一个骄傲的小王子。
       ⑦过了好几天,我和女儿说起那个小男孩举着木珠向我们炫耀的样子时,仍止不住发笑。女儿笑着,笑着,又说了一句:“那个小光头说不定现在又在‘烧包’,向别人炫耀他手上的珠子呢。”我说“有可能”,我笑了,女儿也笑了。

同类题4

阅读理解

Senses That Work Together

    When we think about how our senses work, we usually imagine them operating separately: you sniff a flower, and the smell is delivered uninterrupted from nose to brain. However, it's more complex than that. Most evidence for cross-modal perception (知觉) comes from studies into sound and vision (视觉). But research that shows other senses crossing over is coming out all the time, and it seems that even sound and smell sometimes form an unlikely pairing.

    When New York researchers, Daniel Wesson and Donald Wilson, tried to find out the truth about a “mysterious” area of the brain called the olfactory tubercle (嗅结节),they had to deal with this fact. Originally, they only intended to measure how olfactory tubercle cells in mice responded to smell. But during testing, Wesson noticed that every time he put his coffee cup down with a clunk (哐啷声),the mouse cells jumped in activity. In fact, the olfactory tubercle is well-placed to receive both smell and sound information from the outside world. Later they found that among separate cells, most responded to a smell but a significant number were also active when a sound was made. Some cells even behaved differently when smell and sound were presented together, by increasing or decreasing their activity.

    Of course, mice aren't people, so research team has been carrying out further experiments. They pulled together a group of people and gave them various drinks to smell. Participants were asked to sniff the drinks, and then match them to appropriate musical instruments and produce the notes at different levels. The results were interesting: piano was regularly paired with fruity fragrances; strong smells sounded like the instruments that are made of metal.

    Further research found that listening to different sounds can change your perceptions. Studying taste this time, the team ordered some special toffee (太妃糖)and put together “soundscapes” corresponding to bitterness and sweetness. Participants tasted similar pieces of toffee while listening to each soundscape, and found the toffee more bitter or sweeter, depending on which soundtrack they were listening to.

    Studies like this are helping scientists correctly describe our understanding of the senses, and how the brain combines them with its advantage. The consequences are worth considering. Could we see musicians work together with chefs to produce sound-improved food and drink? Will you be ordering a coffee with a soundtrack to bring out your favorite smell? Come to think of it, that could be one thing you hope coffee shop chains don't get round to.