问题 多选题

如图,小灯泡A、B完全相同,带铁芯的线圈上的直流电阻可忽略,则(  )

A.S闭合瞬间,A、B同时发光,接着A变暗至熄灭,B变的更亮

B.S闭合瞬间,A不亮,B立即亮

C.S闭合瞬间,A、B都不立即亮

D.稳定后在断开S瞬间,B灯立即熄灭,A灯亮一下后熄灭

答案

A、当S闭合瞬间,线圈中磁通量发生变化,导致产生感应电动势从而阻碍电流变化,则两灯立即有电压,同时发光;由于线圈的电阻很小,过会儿A灯被线圈短路,由亮变暗,直到不亮.由于电阻变小,所以B灯渐渐变亮.故A正确;

B、当S闭合瞬间,线圈中磁通量发生变化,导致产生感应电动势从而阻碍电流变化,则两灯立即有电压,同时发光;由于线圈的电阻很小,过会儿A灯被线圈短路,由亮变暗,直到不亮.由于电阻变小,所以B灯渐渐变亮.故B错误;

C、当S闭合瞬间,线圈中磁通量发生变化,导致产生感应电动势从而阻碍电流变化,则两灯立即有电压,同时发光;由于线圈的电阻很小,过会儿A灯被线圈短路,由亮变暗,直到不亮.由于电阻变小,所以B灯渐渐变亮.故C错误;

D、稳定后在断开S瞬间,B灯立即熄灭,由于线圈中电流变化,从而产生感应电动势,对A灯供电,导致A灯亮一下后熄灭.故D正确;

故选:AD

选择题
阅读理解

Disposing(处理)of waste has been a problem since humans started producing it.As more and more people choose to live close together in cities,the waste-disposal problem becomes Increasingly difficult.

During the eighteenth century,it was usual for several neighboring towns to get together to select a faraway spot as a dump site.Residents or trash haulers(垃圾拖运者)would transport household rubbish,rotted wood,and old possessions to the site.Periodically(定期的)some of the trash was burned and the rest was buried.The unpleasant sights and smells caused no problem because nobody lived close by.

Factories,mills,and other industrial sites also had waste to be disposed of.Those located on rivers often just dumped the unwanted remains into the water.Others built huge burners with chimneys to deal with the problem.

Several facts make these choices unacceptable to modern society.The first problem is space Dumps,which are now called landfills,are most needed in heavily populated areas.Such areas rarely have empty land suitable for this purpose.Property is either too expensive or too close to residential(住宅区的) neighborhoods.Long-distance trash hauling has been a common practice but once farm areas are refusing to accept rubbish from elsewhere,cheap land within trucking distance of major city areas is almost nonexistent.

Awareness(意识) of pollution dangers has resulted in more strict rules of waste disposal. Pollution of rivers,ground water,land and air is a price people can no longer pay to get rid of waste. The amount of waste,however,continues to grow.

Recycling efforts have become commonplace,and many towns require their people to take part.Even he most efficient recycling programs,however,can hope to deal with only about 50 Percent of a city’s reusable waste.

小题1:The most suitable title for this passage would be _______.

A.Places for Disposing Waste

B.Waste Pollution Dangers

C.Ways of Getting Rid of Waste

D.Waste Disposal Problem小题2:During the 18th century,people disposed their waste in many ways EXCEPT for _______.

A.burying it

B.recycling it

C.burning it

D.throwing it into rivers小题3:What can be inferred from the fourth paragraph?

A.Farm areas accept waste from the city in modern society.

B.There is cheap land to bury waste in modern society.

C.It is difficult to find space to bury waste in modern society.

D.Ways to deal with waste in modern society stay the same.小题4:The main purpose of writing this article is to _______.

A.draw people’s attention to waste management

B.warn people of the pollution dangers we are facing

C.call on people to take part in recycling programs

D.tell people a better way to get rid of the waste