题干

物理课上,老师做了一个奇妙的“跳环实验”。如图,她把一个带铁芯的线圈L、开关S和电源用导线连接起来后.将一金属套环置于线圈L上,且使铁芯穿过套环。闭合开关S的瞬间,套环立刻跳起。某司学另找来器材再探究此实验。他连接好电路,经重复试验,线圈上的套环均末动。对比老师演示的实验,下列四个选项中,导致套环未动的原因可能是(   )

A:线圈接在了直流电源上

B:电源电压过高

C:所选线圈的匝数过多

D:所用套环的材料与老师的不同

上一题 下一题 0.0难度 选择题 更新时间:2016-08-17 10:19:42

答案(点此获取答案解析)

D

同类题1

阅读理解

“The first and best of victories for a man is to conquerhimself; to be conquered by himself is, of all things, the most shameful,” saysPlato. Self-control is at the root of all the advantages. Let a man give in tohis impulses (冲动) andfeelings, and from that moment he gives up his moral freedom.

A single angry word has lost many friends. When Socrates foundin himself any temper or anger, he would check it by speaking low in order tocontrol himself. If you are conscious of being angry, keep your mouth shut sothat you can hold back rising anger. Many a person has dropped dead in greatanger. Fits of anger bring fits of disease. “Whoever the gods would destroy,they first make them mad.” “Keep cool,” says Webster, “anger is notargument.” “Be calm in arguing,” says George Herbert, “for fierceness (狂怒) makes error a fault.”

To be angry with a weak man is to prove that you are not strongyourself. “Anger,” says Pythagoras, “begins with foolishness and ends withregret.” You must measure the strength of a man by the power of the feelings heconquers, not by the power of those which conquer him.

Self-control is man’s last and greatest victory.

If a man lacks self-control he seems to lack everything. Withoutit he can have no patience, no power to govern himself; he can have noself-confidence, for he will always be controlled by his strongest feeling. Ifhe lacks self-control, the very backbone and nerve of character are lackingtoo.