问题 选择题

关于电场力和电场强度,以下说法正确的是(  )

A.两个点电荷分别处于电场中的A、B两点,电荷受到的电场力大处则场强大

B.在电场某点如果没有检验电荷,则电场力为零,电场强度也为零

C.检验电荷在电场中某点受到的电场力为零,则该点的场强为零

D.一检验电荷在以一个点电荷为球心,半径为r的球面上各点所受电场力相同

答案

A、电场强度取决于电场本身,与有无试探电荷无关,场强公式E=

F
q
,只是为研究电场的方便,采用比值法下的定义;据场强的定义式E=
F
q
,知,同一点电荷分别处于电场中的A、B两点,电荷受到的电场力大则场强大,而两个点电荷的电量不一定相等,故A错误.

B、电场强度取决于电场本身,与有无试探电荷无关,场强公式E=

F
q
,只是为研究电场的方便,采用比值法下的定义,所以在电场某点如果没有检验电荷,该点的场强不变,故B错误.

C、据场强的定义式E=

F
q
,知,电场中某点场强为零,则检验电荷在该点受到的电场力为零,故C正确.

D、根据点电荷的场强公式E=

kQ
r2
知:电场强度只由场源电荷电量和位置决定,且检验电荷在以一个点电荷为球心,半径为r的球面上各点场强大小相同,但方向不同,所以半径为r的球面上各点所受电场力不相同,故D错误.

故选:C.

单项选择题
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 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 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 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 the 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