问题 问答题

在断电自感现象中,为什么开关断开后,灯泡的发光会持续一段时间,甚至会比原来更亮?试从能量的角度加以讨论。

答案

在断电自感现象中,开关断开前,线圈中有电流,则线圈中具有磁场能;开关断开后,线圈中产生阻碍电流减小的自感电动势,把磁场能转化为电能,通过线圈给灯泡供电消耗了这些电能。所以,开关断开后,灯泡仍能发一会儿光,延迟熄灭。如果自感电流大于灯的原电流,灯会比原来更亮。可见断开开关后,灯再发光的能量并不是凭空产生的,而是通过自感现象将原来储存在线圈中的磁场能转化为电能,供给电灯发光的,这一转化满足能量守恒定律。

完形填空
A strong wind was blowing hard, thunder could be heard, and lightning flashed    the dark sky. Rain was pouring down;it looked     heaven had been broken open.
Gleams of light(微弱的闪光) appeared from     of faraway houses, shining like jewels in all the dark.
A    woman dressed in rags(衣衫褴褛) and trembling with cold was    on a lonely road, while the merciless rain was    her without stop.
She knocked at a door, and a    answered it. She begged him to let her stay a while    . The boy    let her into the sitting room and leave her sitting by the fire.
The woman appeared old and tired under the bright electric light,      she was only in her early thirties. She sat       for a moment, and then her eyes began to look about the    . When her eyes rested on the picture of a young man, she    up, looking thunderstruck.
Just then, the boy came with his    . The man at once recognized the woman as his wife. They had     touch with each other during the war,      he thought he had lost her forever.
     words needed to be spoken. They ran into each other’s arms    the boy stared at them,puzzled.
The storm was over and the sky cleared. Feeling very    , the couple stood face to face with their child between them, watching the rain as it gradually    .
小题1:
A.intoB.belowC.acrossD.through
小题2:
A.only if B.as ifC.what ifD.even if
小题3:
A.doorsB.roofsC.wallsD.windows
小题4:
A.poorB.prettyC.uglyD.rich
小题5:
A.cryingB.wanderingC.strugglingD.wondering
小题6:
A.strikingB.beating C.hittingD.flowing
小题7:
A.boyB.girlC.manD.woman
小题8:
A.nearB.outC.outsideD.inside
小题9:
A.firstB.thenC.nowD.last
小题10:
A.becauseB.soC.thoughD.However
小题11:
A.stillB.thirstyC.hungryD.straight
小题12:
A.pictureB.fireC.roomD.house
小题13:
A.lookedB.cameC.pickedD.stood
小题14:
A.brotherB.fatherC.sisterD.mother
小题15:
A.madeB.gotC.keptD.lost
小题16:
A.whoB.whichC.butD.and
小题17:
A.SomeB.NotC.NoD.Many
小题18:
A.whileB.asC.whenD.since
小题19:
A.happyB.disappointedC.sorryD.calm
小题20:
A.beganB.stoppedC.endedD.finished
单项选择题