感应电流一定和原电流方向相反

线圈中产生的自感电动势较大的其自感系数一定较大

自感电动势总是阻碍原来电流的变化

对于同一线圈，当电流变化越大时，线圈中产生的自感电动势也越大

感应电流一定和原电流方向相反

线圈的自感系数大，它的自感电动势一定大

对于同一线圈，当电流变化较大时，产生的自感电动势也较大

对于同一线圈，当电流变化较快时，产生的自感电动势也较大

It has been estimated that there are more than 20 million Americans in this category, 10% of the population, including many millions of whites.

Blacks are gaining in self-confidence. In more and more areas they are winning control of their communities, and their standard of living is going up faster than that of the poor whites. It is still a hard struggle. There is still prejudice and even some hatred, but in most walks of American life there are now more blacks than ever before.

The era of blatant discrimination ended in the 1960s through the courageous actions of thousands of blacks participating in peaceful marches and sit-ins, to force Southern states to implement the Federal desegregation laws in schools and public accommodations. Down came the 'whites only' notices in bused, hotels, trains, restaurants, sporting events, restrooms and on park benches that once could be found everywhere throughout the South. Gone were the restrictions that prevented blacks voting. Gone, too, were the hideous lynchings, which since the Civil War had caused the death of thousands of innocent blacks—hanged without trial by white mobs. However, even today, poor, uneducated lacks do not always receive the same degree of justice that the more affluent and better educated can expect.

Many blacks chose to keep silent about their unfairness instead of resorting to violence. But their silence was also problem provoking: on the one hand, silence would build up a lot of complaints and hatred in their minds, thus resulting in a negative approach to lif

职业病

生物地球化学性疾病

环境污染

流动人口的增加

正确

错误

感应电流一定和原电流方向相反；

线圈中产生的自感电动势较大的其自感系数一定较大；

对于同一线圈，当电流变化越大时，线圈中产生的自感电动势也越大；

自感电动势总是阻碍原来电流变化的。

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自感电动势总是阻碍原来电流变化的

感应电流一定和原来电流方向相反

线圈中产生的自感电动势较大，它的自感系数也一定大

对于同一线圈，电流变化越大时，产生的自感电动势也越大

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