问题 选择题

图中EF、GH为平行的金属导轨,其电阻可不计,R为电阻器,C为电容器,AB为可在EF和GH上滑动的导体横杆.有均匀磁场垂直于导轨平面.若用I1和I2分别表示图中该处导线中的电流,则当横杆AB(  )

A.匀速滑动时,I1=0,I2=0

B.匀速滑动时,I1≠0,I2≠0

C.加速滑动时,I1=0,I2=0

D.加速滑动时,I1≠0,I2≠0

答案

当AB切割磁感线时,相当于电源.匀速滑动,电动势不变,电容器两端间的电压不变,所以I2=0,I1≠0;加速滑动,根据E=BLv,知电动势增大,电容两端的电压增大.所带的电量要增加,此时有充电电流,所以I1≠0,I2≠0.故A、B、C错误,D正确.

故选D.

完形填空

Are only clever and good-looking students happy in the school? Best-selling ___31___ Xiao Nizi (Nini) doesn’t think so.

___32___ has his own place in the sky." she said.  "We're all special in our ownways.”

Nini, from Hunan, writes stories about young people in the school. Her books,___33___ Devils Kiss and Un-e on Midsummer’s Night, are very ___34___ with students.

In her stories, the main characters arc usually common girls who are neither pretty ___35___ smart. But they always win the love of a Prince Charming(白马王子),or___36___ successful stars.

"It’s not because of luck."' said Nini. ""They are ___37___ honest and they don't lie. They know what they arc good___38___ and work hard to realize their dreams. "

Nini herself is like one of the characters in her stories. She was a shy girl at school. But she thought a lot and liked languages, and that made her ___39___ to be a writer. She hopes her stories ___40__ make more kids happy.

小题1:A. writer        B. reader         C. speaker

小题2: A. Nobody     B. Everyone      C. Someone

小题3:A. as           B. for example    C. such as

小题4: A. successful    B. popular        C. funny

小题5: A. nor          B. or            C. but

小题6:A. become      B. make         C. take

小题7: A. still          B.only         C. ever

小题8: A. at           B. for           C. with

小题9:A. deciding      B. to decide      C. decide

小题10: A. can          B. must        C. need

选择题