问题 选择题

如图所示电路电源电压不变。开关S闭合前,电压表示数为6V;开关S闭合后,电流表A1的示数为0.6A,A2的示数为0.5A,R2R3=2∶1。下列判断正确的是

A.电阻R1R2的阻值比为3∶2

B.电阻R2消耗的电功率为1.2W

C.电路消耗的总功率为6.6W

D.电阻R1的阻值为30W

答案

答案:B

题目分析:(1)由图知,开关断开时,电压表测量的是电源电压,因示数为6V,可知电源电压为6V;

(2)开关S闭合后,等效电路图如下图所示:

∵三电阻并联,且R2:R3=2:1

∴根据I=可得,I2:I3=R3:R2=1:2,

∵电流表A1的示数为0.6A,

∴I2=0.2A,I3=0.4A,

∵电流表A2的示数为0.5A,

∴I1=0.3A,

干路电流I=I1+I2+I3=0.3A+0.2A+0.4A=0.9A,

∵R=

∴R1:R2=I2:I1=0.2A:0.3A=2:3,故A不正确;

电阻R2消耗的电功率P2=UI2=6V×0.2A=1.2W,故B正确;

电路消耗的总功率P=UI=6V×0.9A=5.4W,故C不正确;

R1==20Ω,故D不正确.

点评:本题考查了学生对并联电路的电流特点、欧姆定律和电功率公式的掌握和运用,分析电路图得出当开关闭合时三电阻并联是本题的关键

阅读理解

阅读理解。

     Astronauts aboard the space station celebrated a space first on Wednesday by drinking water that had

been recycled from their urine (尿), sweat and water got from air. They said "cheers" to NASA workers

on the ground.

     The urine recycling system is needed for astronaut stations on the moon and Mars. It also will save

NASA money because it won't have to ship up as much water to the station by space shuttle or cargo rocket.

Besides, it's important as the space station is about to expand (扩大) from three people living on board to

six.

     The recycling system had been brought up to the space station last November, but it couldn't be used

until samples (样品) were tested back on earth. So when it came time to actually drink up, NASA made a

big deal of it. The three-man crew stood holding their drinks and congratulated engineers in two NASA

centers that worked on the system.

     "This is something that had been the stuff of science fiction," American astronaut Michael Barratt said

before taking a small mouthful. The taste is worth trying.

     The new system takes the combined urine of the crew from the toilet and moves it to a big tank, where

the water is boiled off, and the vapor is collected. The rest of the urine is thrown away. Then the water

vapor is mixed with water from air, and then it goes through filters (过滤器). When six crew members are

aboard, it can make about six gallons from urine in about six hours.

     "Some people may find the idea of drinking recycled urine distasteful, but it is also done on earth, but with

a lot longer time between urine and the tap," said Marybeth Edeen, the space station's national lab manager.

     The technology NASA developed for this system has already been used for quick water purification (净化)

after the 2004 Asian tsunami.

1. According to the text, the recycling system is important because _____. [ ]

A. it makes traveling to the moon for the average person possible

B. with it NASA won't need to ship any water up to the space station

C. it protects the environment in space by reducing the amount of waste

D. it can help meet the need for more water after the crew is expanded

2. Which is the RIGHT time order of the following events?

    a. The samples of the recycled water were tested on earth.

    b. Astronauts celebrated the space's first making water from urine.

    c. The recycling system was brought up to the space station.

    d. The technology for the system was used to quickly purify water. [ ]

A. a, d, c, b

B. a, c, b, d

C. d, c, a, b

D. d, a, c, b

3. From Paragraph.5 we can know _____. [ ]

A. the process of recycling urine

B. the effect of the recycling system

C. an opinion on recycling urine

D. the theory behind the recycling system

4. What is the best title for the text? [ ]

A. Drink up: Space Station Recycles Urine to water

B. New Technology Is Used in the Space Station

C. The Research of NASA Has Made Great Progress

D. Good News: Water Recycled from Urine Tastes Good

填空题