请你选择出适当的器材，设计一个电路，用来测量两个电流表的内电_爱下问搜题

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问题实验题

请你选择出适当的器材，设计一个电路，用来测量两个电流表的内电阻。要求方法简单，有较高的测量精度。

A．待测电流表：量程为50mA，内电阻约几十欧姆

B．待测电流表：量程为30mA，内电阻约几十欧姆

C．电压表V：量程15V，内电阻为=15kΩ

D．电阻箱：阻值范围0~9999.9Ω

E．电阻箱：阻值范围0~99.9Ω

F．滑动变阻器：最大阻值150Ω，额定电流1.5A

G．滑动变阻器：最大阻值20Ω，额定电流2A

H．定值电阻：阻值40Ω，功率0.5W，作保护电阻用

I．电池组E：电动势12V，内电阻约0.5Ω J

单刀单掷开关若干、导线若干。

（1）将你设计的电路图画在虚线框内；

（2）选用的器材为_______；（填字母序号）

（3）实验中需要测量的物理量是_____________；

（4）分别写出计算两只电流表内电阻的表达式：=____________、=____________。

答案

（1）

（2）A，B，C，D，G，I，J

（3）闭合开关S，调节滑动变阻器和变阻箱之值，读出电流表和的示数和，电压表示数U，变阻器阻值R

（4）；

完形填空

Have you ever had to decide whether to go shopping or stay home and watch TV on a weekend? Now you   36  do both at the same time. Home shopping television networks have become a   37  for many people to shop without   38        having to leave their homes.
Some shoppers are   39  of department stores and supermarkets — 40
the crowds, waiting in long lines, and sometimes having slight   41  of finding anything they want to buy. They’d rather sit quietly at home in front of the TV set and   42  a friendly announcer describe a product 43  a model shows it. And they can   44  around the clock, buying something 45  by making a phone call.
Department stores and even mail-under companies are   46  to join in the success of home shopping. Large department stores are busy   47  their own TV channels to encourage TV shopping in the future.   48  can ask questions about products and place   49 , all through their TV sets.
Will shopping by television   50  take the place of shopping in stores? Some industry managers think so.   51  many people find shopping at a   52  store a great enjoyment. And for many shoppers, it is still important to   53  or try on dresses they want to buy. That’s   54  specialists say that in the future, home shopping will   55  together with store shopping but will never entirely replace it.

D．fortunately

问答题简答题

古代四美指什么？