题干

图甲是某生产流水线上 的产品输送及计数装置示意图。其中S为激光源,Rl为光敏电阻(有光照射时,阻值较小;无光照射时,阻值较大),R2为定值保护电阻,a、b间接“示波器”(示波器的接入对电路无影响)。水平传送带匀速前进,每当传送带上的产品通过S与Rl之间时,射向光敏电阻的光线会被产品挡住。若传送带上的产品为均匀正方体,示波器显示的电压随时间变化的关系如图乙所示。己知计数器电路中电源两极间的电压恒为6V,保护电阻的阻值为400Ω。则  (      )

A:每1 h通过S与Rl之间的产品个数为6000个

B:有光照射和无光照射时保护电阻R2两端的电压之比为1:2

C:有光照射和无光照射时光敏电阻的阻值之比为1:2

D:有光照射时光敏电阻Rl的阻值为800Ω

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A

同类题5

阅读下面短文,然后回答问题。

    Wang Fei,a Chinese student,and Mary,an American student studying Chinese in China,were in a supermarket.They saw a young man walking down the stairs.In his hurry,he missed the last two steps and fell onto the ground.He tried to stand up while people around him laughed.Luckily,he seemed to be OK.

    Mary found Wang Fei smiling a little and was not happy about it. “Tell me, Fei, how could people laugh when someone fell like that? Why didn't they go up and ask him if he was hurt?”

    Wang Fei said, “Because they knew he wasn't hurt too much.”

    “But I still don't understand.A fall is a fall.In my culture, people would never laugh!”

    This is an example.The Chinese and the westerner will think and act differently when seeing such a thing.Chinese people are used to laughing or smiling.Very often the person who is in embarrassing(困窘的)situation would also laugh or smile to get out of it.However,if someone gets hurt seriously,it will not be a laughing matter any more.People will help him or her instead.

    But,in that case,a westerner will rush over and help the person get up.If a westerner falls,he or she,like a Chinese person,may try to make a joke if he or she is not hurt.If two close friends are walking together,and one falls but clearly isn't hurt,a common joke is to say “Have a nice trip”.

    So different people have different habits and different countries have different cultures