问题 填空题

现有两只定值电阻R1、R2,已知R1=2R2,一个能向外提供恒定电压的电池组,还有若干导线.

(1)试把以上器材分别画在下页的甲图和乙图中标有A、B、C、D字样的接线柱上,使它们各自组成一个完整的电路(所用电表均为理想电表,量程也总能满足要求).并能满足以下要求:当电键S断开时,电表指针偏转到某一位置,当电键S闭合时,电表的示数为S断开时的3倍.

(2)在满足以上要求的情况下,图甲中电键S断开和闭合两种情况下,外电路消耗的电功率之比为______.

(3)在满足以上要求的情况下,图乙中电键S断开和闭合两种情况下,R2上消耗的电功率之比为______.

答案

(1)虚线框内有电源和两个电阻串联,让开关与电阻R1并联,电路如图所示.

(2)设R1=2R2=2R,

电键S断开时,R1、R2串联,总电阻为3R,此时的总功率为P1=

U2
3R

电键S闭合时,只有电阻R2,总电阻为R,此时的总功率为P2=

U2
R

所以外电路消耗的电功率之比为 1:3.

(3)电键S断开时,R1、R2串联,总电阻为3R,并且R1=2R2,此时R2的功率为

1
3
P1=
U2
9R

电键S闭合时,只有电阻R2,总电阻为R,此时的总功率即为R2的功率,即为P2=

U2
R

所以R2上消耗的电功率之比为1:9.

故答案啊为1:3,1:9.

问答题 简答题
阅读理解

阅读理解。

    Willa Cather once said, "When people ask me whether writing has been a hard or easy

road,I always answer with the famous saying: The end is nothing;the road is all. That is

what I mean when I say writing has been a pleasure. I have never used the computer with

the thought that one more task had to be done."

    Like most writers, Willa Cather did not write books for the money that they brought her,

but rather for the pleasure that came in their writing. Her works were, like her, simple and

full of the vigor of her days in Nebraska, where she grew from child to young womanhood

and where she developed a deep love for the treeless land of the great plain with its wild

flowers, wheat fields and rivers.

    "It's a rather strange thing about the flat country," she wrote later. "It takes hold of you or

it leaves you perfectly cold. A great many people find it very dull; they like a church tower,

an old factory, a waterfall, the country all made to look like a German Christmas card...But

when I come to the open plain, something happens. I'm home. I breathe differently."

1. Willa Cather wrote because she found writing _____. [ ]

A. simple and lively

B. opened up a road to success

C. neither too hard nor too easy

D. interesting and enjoyable

2. What was the place like where Cather grew up? [ ]

A. It was cold,plain and without a church.

B. It was vast,open and flat.

C. It was like a German Christmas card.

D. It was a colorful world of wild flowers.

3. When she said "It takes hold of you or it leaves you perfectly cold.", Willa Cather

    meant that _____. [ ]

A. you either love the place or hate it

B. you decide either to stay or to leave

C. some find the place warm; others find it cold

D. some find the place peaceful; others find it wild

4. What happens when Cather comes to the open plain? [ ]

A. She breathes differently from others.

B. She wants to make the place her home.

C. She feels completely comfortable.

D. She finds the place similar to her home.