问题 填空题

图所示的电路中,R1、R2均为定值电阻.电源电压不变.闭合开关S1、S2,两电表均有示数;再断开开关S2,则电流表示数    ,电压表示数    ,电压表与电流表示数之比    

(本题每空均选填“变大”、“变小”或“不变”)

答案

变小 变小  不变

题目分析:当闭合S1、S2,R1被短路,电压表测量电源电压(R2两端的电压);再断开S2,R1被串联接入电路,电路中总电阻变大,电源电压不变,电路中电流变小,电压表仍测量R2两端的电压,其示数也减小;两次均测量R2两端的电压,对同一电阻,通过的电流与加在两端的电压成正比,所以电压表的示数与电流表的示数的比值不变.

点评:分析开关开闭问题时应注意:当开关断开时,与之相连的用电器将去掉不能工作;当开关闭合时有两种情况:一是与之相连的用电器将被接入电路,二是与开关并联的用电器将被短路不能工作,改变电压表的测量对象.

填空题
阅读理解

When you think of the different types of advertising, several come to your mind. There are the traditional means to advertise: newspapers, magazines, radio, television commercials, billboards, and even taxicabs. Yet there are other types of advertising, such as aerial advertising, which is very different in many aspects.

Radio advertising is aimed at the local customers. The downside of using radio is that the customer needs to have the station tuned in. Placement of ads on the radio is another consideration since listening time is important to the ad being heard at the best time. The upside of using radio is that the audience does tend to remember jingles(收音机广告中的歌曲)that are easy to remember.

Magazine and newspaper advertising is directed to the subscribers(订阅人). The subscriptions limit the availability to non-subscribers. The concept of being able to read information online is slowly changing the subscriptions to this advertising market. Limitations of circulation of magazines and newspapers mean fewer people viewing the advertisements.

Television commercial advertising is channeled to the viewers. Limitations of viewers based on the available channel selections lower the exposure audience. With the availability of satellite to consumers, locating the client base for advertisement can easily be lost or overlooked.

Billboard advertising focuses on the area of the billboard. Limitations of outside regions viewing the information are high. Getting the attention of the passers-by to view the information is also a subject to be considered.

Aerial banner advertising focuses on vast population of various regions. Based upon the region, the exposure is limitless. Grabbing or gaining the public’s attention is based on simple human nature to look up at the airplane that is flying overhead. People typically look up when a plane flies overhead. To have a banner with an advertisement adds more curiosity and response.

People tend to remember aerial advertising at a high rate. They also tend to communicate to others about the advertisement by sharing the information by word of mouth. This word of mouth is absolutely free but is of important benefit to aerial advertising. Aerial advertising can be done throughout the entire year, but the warmer months are preferred. Aerial advertising has certain restrictions. Yet these restrictions are fewer than the other means of advertising.

59.The underlined word“downside”in the second paragraph can be replaced by ________.

A.strength       B.weakness     C.purpose           D.instruction

60.Which of the following is the author probably in favor of?

A.Radio advertising.      B.Television advertising.

C.Aerial advertising. D.Billboard advertising

61.The first paragraph is used as a(n) _________.

A.explanation   B.introduction         C.account           D.start

62.What does the passage mainly tell us?

A.Different advantages of advertising.      B.Advantages overpass weakness.

C.Various weaknesses of advertising.  D.Different types of advertising.