题目

同学们自制电磁铁并连接了如图所示的电路．闭合开关后，为了能够吸引更多的小铁钉，变阻器的滑片应向      （填“C”或“D”）端移动，如图中的甲端是电磁铁的      极． 答案：C，N 【解析】 试题分析：电磁铁的磁性强弱与电流的强弱有关，故为了增强电磁铁的磁性应增大电路中的电流，则由滑动变阻器的接法可知滑片的移动方向； 由右手螺旋定则可知电磁铁的磁极． 【解析】 要想吸引更多的小铁钉应增大磁性，因电磁铁的磁性与电流强弱有关，故应增大电路中的电流，则 阅读理解 　　If you ask some people, “How did you learn English so well?” you may get a surprising answer：“In my sleep!” 　　These are people who have taken part in one of the recent experiments(实验)to test the learn-while-you-sleep method(方法), which is now being tried in several countries, and with several subjects．English is among them． 　　Scientists say that this sleep-study method greatly speeds language learning．They say that the ordinary person can learn two or three times as much during sleep as in the same period during the day－and this does not affect(影响)his rest in any way．However, sleep-teaching will only put into your head what you have studied already while you are awake． 　　In one experiment, ten lessons were broadcast over the radio for two weeks．Each lesson lasted twelve hours－from 8 p.m.to 8 a.m．The first three hours of English grammar and vocabulary(词汇)were given with the students awake．At 11 p.m.a lullaby(催眠曲)was broadcast to send the student to sleep and for the next three hours the radio in a soft and low voice broadcast the lesson again into his sleeping ears．At 2 a.m.a sharp noise was sent over the radio to wake the sleeping student up for a few minutes to go over the lesson．The soft music sent him back to rest again while the radio went on．At 5 o’clock his sleep ended and he had to go through the lesson again for three hours before breakfast． (1) By the learn-while-you-sleep method, one ________． [　　] A． starts to learn a new lesson in sleep B． learns how to sleep better C． is made to remember his lesson in sleep D． can listen to the radio broadcast while lying in bed (2) In the experiment, lessons were given ________． [　　] A． in the night time B． after lullabies were broadcast C． while the student was awake D． all through the twelve hours (3) Before each lesson finishes, the student has to ________． [　　] A． get up and take breakfast B． be woken up by a loud voice C． listen to the lesson again in sleep D． review(复习)the lesson by himself (4) The sleep-study method is being tried in many countries to teach ________． [　　] A． the English language B． grammar and vocabulary C． a number of subjects D． foreign languages