问题 填空题

如图所示的电路中,电池的电动势为E,内阻为r,电路中的电阻R1、R2和R3的阻值都相同,在电键S处于闭合状态下,若将电键S1由位置1切换到位置2,则电压表示数将______,电池内部的功率将______(以上空格均选填“变大”、“不变”或“变小”).

答案

1.将电键S1由位置1切换到位置2,外电阻变小,电动势和内阻不变,电路中的总电流变大,内电压变大,外电压变小,电压表测的是外电压,所以电压表示数变小.

2、电路中的总电流变大,根据P=I2r,知,电源内部消耗的功率变大.

故答案为:变小;变大.

单项选择题
阅读理解

In the world today, there are millions of surveillance cameras, or “spy cams”, watching and monitoring our daily activities. There are some benefits of course, as people who are breaking laws can be watched and caught using cameras and this helps keep our society and public places safe. These cameras are everywhere and most are openly visible on roads, in airports, businesses, shopping centers and government buildings and even in lifts. Even schools have started using spy cams to watch student activity and behaviour.

The cameras are so common now that we hardly ever even notice them. But the problem lies with the ones that are hidden away from our eyes and are unseen. Technology has helped develop tiny cameras that can be very well hidden and they can “spy” on shoppers, workers, babysitters and people in hotels and clubs without the people even knowing.

It is these spy cams that people feel are an invasion of privacy. Recently, in the US, there have been a number of court cases against babysitters whose actions have been recorded by their employers on hidden cameras.

The number of cameras in public and private areas is on the increase and with rising crime rates and the recent terrorist attacks, more and more surveillance cameras are being used to watch us. This means that we all have to be aware that our employers, department stores, police and even some of our friends could be spying on us at any time!

小题1:In the writer’s opinion, surveillance cameras _______.         .

A.do more good than wrong

B.are overused

C.should be very popular

D.ought to be more widely used小题2:In what way can the surveillance camera benefit the public?

A.By helping keep social safety.

B.By monitoring the employees.

C.By watching the students in class.

D.By spying on customers.小题3:According to Paragraphs 3 and 4, people _______ the use of hidden cameras.

A.object to

B.agree to

C.feel happy about

D.are fearful of小题4:Spy cams will be more widely used in the future because _______.         .

A.all people want to spy

B.of the invasion of privacy

C.people enjoy being watched

D.of terrorist attacks