问题 计算题

小明同学为邻居王大爷的屋顶水池设计了一个测定水池内水面高度的装置,浮标高度与滑动变阻器R的金属滑片下移(或上移)的距离成正比.R0=12欧,电源电压为6V,水量表由量程适中的电流表充当.池内水深为0.5H时,金属滑片正好在R的中央,如图所示,此时电流表示数为0.3A;池内水深H时,电流表示数为0.4A.

①滑动变阻器R的总电阻为多大?

②当电流表的示数为多少时表示池中的水已全部流出?

答案

解:

(1)Ω,R=16Ω;

(2)当电路中电流为0.4A时,滑动变阻器接入电路的电阻为Ω=Ω=3Ω;

又因为浮标高度与滑动变阻器R的金属滑片下移(或上移)的距离成正比,当浮标从0.5H到H时,滑动变阻器的电阻变化为8Ω﹣3Ω=5Ω,所以当池中水全部流出时,浮标从0.5H到0,因此滑动变阻器的阻值变化仍然为5Ω.所以当池中水全部流出时,滑动变阻器接入电路中的电阻为:

8Ω+5Ω=13Ω;

即电流表的示数为:

阅读理解

Bicycle tour and race

A bike tour and race will be held on August 26 and 27( Sat. &Sun.)at 5:30 am, the riders will leave Tian’an Men Square and ride the first 35 kilometers as a training leg. Then the next 55 kilometers leg, from Yanjiao to Jixian, will be the first competitive part of the tour. The riders and their bikes will then be taken from Jixian to Changli.

The second racing leg of the tour will be from Changli to seaside of Nandaihe, covering a distance of 20 kilometers. Saturday night includes the stay at Nandaihe and supper. Sunday morning is free for play at the seaside. At noon all the people and their bikes will be taken back to Beijing.

Cost: 200 yuan

Telephone: 4675027  

Brazilian footballers  

The Brazilian Football Club play Beijing Guo’an Team at the Workers Stadium on August 26.The club has four nation team players. Also coming is 1994 US World Cup star Ronario who has promised to play for at least 45 minutes.

Ticket prices: 60,100, 150 yuan

Time /date: 4:30 pm, August 26(Sat.)

Telephone: 5012372

Rocking climbing

The third National Rock Climbing Competition will be held on August 26~27 at the Huairou Mountain-climbing Training Base. More than 10 teams from Beijing, Wuhan , Dalian , Jilin and other places will take part in it. A Japanese team will give an exhibition climbing. Free for spectators(观众).

Take a long-distance bus from Dongzhimen to Huairou.

Time/Date: 9~12 am, August 26 and 27

Telephone: 7143177, 7144850 Wang Zhenghua

60. The main purpose of announcing the above events is to give information about _________.

A. visiting teams                    B. famous players

C. things to do for the weekend       D. prices to pay for the sports events.

61. If you take part in the bike tour, you will ride for _________

A. 35 kilometers     B. 55 kilometers    C. 75 kilometers     D. 110 kilometers

62. What is special about the rock climbing competition?

A. Many foreign teams take part in it. 

B. You can watch it without paying.

C. You don’t have to be a sportsman to take part in.

D. The bus trip to the places of the competition is free.

63. If you want to do something on Saturday afternoon, which telephone number will you call?

A. 4675027    B. 7143177    C. 5012372  D. 7144850

单项选择题