题干

【2012•广东模拟】北半球地磁场的竖直分量向下.如图所示,在北京某中学实验室的水平桌面上,放置边长为L的正方形闭合导体线圈abcd,线圈的ab边沿南北方向,ad边沿东西方向.下列说法中正确的是(  )

A:若使线圈向东平动,则b点的电势比a点的电势低

B:若使线圈向北平动,则a点的电势比b点的电势低

C:若以ab为轴将线圈向上翻转,则线圈中感应电流方向为a→b→c→d→a

D:若以ab为轴将线圈向上翻转,则线圈中感应电流方向为a→d→c→d→a

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C

同类题1

   A ban on smoking in most public places goes into effect(效果) on Sunday in China - home to a third of the world's smokers. That means around 300 million smokers will no longer be allowed to light their cigarettes in the "enclosed public places." These include hotels, restaurants, theaters and public transport waiting rooms. The ban does not cover offices or factories.
   The campaign is aimed at controlling(控制) the number of deaths from smoking-related illnesses, running at a million a year. According to the World Health Organization, more than 3,000 people die every day in China because of smoking. Health experts also hope it will help Chinese to raise the knowledge of the dangers of smoking.
   But the new rules have been criticized because they do not include punishments(处罚) for those who choose not to obey them.Most people worry that Chinese smoking ban may have little effect.
   Business owners often hate rules that force(强迫) them to ban smoking on their restaurants, bar, cafe..., because many customers(顾客) do not like the rules and complain. Often you find people smoking at the next table while you are eating your meal or having a drink in a bar.
It appears that many Chinese people don't know the dangers of smoking. Research suggests only one in four knows the harm(害处) cigarettes or second-hand smoke can cause.
   At the same time the government makes a lot of money from the sales of cigarettes by the state-owned firms that make and sell all tobacco products throughout the country.