问题 多选题

如图所示电路中,电源内阻不能忽略,电流表、电压表都是理想电表,当滑动变阻器R0的滑片P从a端移到b端的过程中(  )

A.电压表示数先减小后增大,电流表示数不断增大

B.电压表示数先增大后减小,电流表示数不断减小

C.电压表示数先增大后减小,小灯亮度先变暗后变亮

D.电压表示数先增大后减小,流过滑动变阻器Pb部分电流不断增大

答案

当滑动变阻器R0的滑片P从a端移到b端的过程中,变阻器总电阻先增大后减小,路端电压先增大后减小,则电压表先增大后减小.

当滑动变阻器R0的滑片P从a端移到中点的过程中,变阻器总电阻增大,干路中电流减小,变阻器的电压增大,而变阻器Pb部分的电阻减小,则变阻器Pb部分的电流增大,所以通过通过Pa部分的电流减小.

当滑动变阻器R0的滑片P从中点移到b端的过程中,变阻器总电阻减小,干路中电流增大,变阻器的电压减小,变阻器Pa部分的电阻增大,所以通过通过Pa部分的电流减小,则通过滑动变阻器Pb部分电流不断增大.故电流表的读数减小.故电流表示数不断减小.

干路电流先减小后增大,则灯亮度先变暗后变亮.

所以电压表示数先增大后减小,电流表示数不断减小,小灯亮度先变暗后变亮,流过滑动变阻器Pb部分电流不断增大.故A错误、BCD正确.

故选BCD.

阅读理解

All around the world, people drink tea. But tea doesn’t mean the same thing to everyone. In different countries people have different ideas about drinking tea.

People in China like to drink tea with nothing in it, and they often have it with their friends or by themselves. They have two kinds of tea—green tea and black tea. They may drink tea at any time of the day anywhere. But they don’t drink tea just before they go to bed, for tea makes them awake.

In England, people like to drink tea with milk and sugar in it, and they often have it in the afternoon with their friends.

In Japan, people also like drinking tea very much. It is very popular there. They drink tea every day. They have it in different ways from that in China. Some young Japanese girls are good at making tea. They can do it beautifully.

In the U.S.A., people drink tea at breakfast or after meals. They usually use tea bags to make their tea. Making tea with tea bags is faster and easier than making it with tea leaves in teapots.

小题1:People in ________ like to drink tea with milk and sugar in it.

A. England      B. China        C. the U.S.A.      D. Japan

小题2:Why don’t people often drink tea before they go to bed in China?

A.Because they are full.

B.Because they may not sleep well.

C.Because there is nothing in the tea.

D.Because there is some milk and sugar in it.小题3:In which country do people usually make tea with tea bags?

A. In England.  B. In China.    C. In the U.S.A.    D. In Japan.

小题4:Chinese people like to drink ________.

A.tea with anything in it

B.milk and sugar in it

C.tea with tea bags in it

D.tea with nothing in it小题5:What does “black tea” mean in Chinese? It means ________.

A.浓茶

B.黑茶

C.红茶

D.绿茶

综合题