问题 选择题
如图所示,两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R,导轨电阻可忽略不计;MN为放在ab和cd上的一导体杆,与ab垂直,其电阻也为R;整个装置处于匀强磁场中,磁感应强度的大小为B,磁场方向垂直于导轨所在平面(指向图中纸面内);现对MN施力使它沿导轨方向以速度v(如图)做匀速运动;令U表示MN两端电压的大小,则(  )

A.U=vBl,流过固定电阻R的感应电流由b到d

B.U=vBl,流过固定电阻R的感应电流由d到b

C.U=vBl,流过固定电阻R的感应电流由b到d

D.U=vBl,流过固定电阻R的感应电流由d到b

答案

答案:A

阅读理解

In almost every big university(大学)in the United States, football is a favourite sport. American football is different. Players sometimes kick the ball, but they also throw the ball and run with it. They try to take it to the other end of the field. They have four chances(机会)to move the ball ten yards(码). They can carry it or they can throw it. If they move the ball ten yards, they can try to move it another ten yards. If they move it to the end of the field, they receive six points.

It is difficult to move the ball. Eleven men on the other team try to stop the man with the ball. If he does not move the ball ten yards, his team kicks the ball the other team.

Each university wants its own team to win. Many thousands of people come to watch. They all shout for their favourite team.

Young men and women come on the field to help the people shout more. They dance and jump while they shout.

Each team plays ten or eleven games each season.

The season begins in September and ends in November. If a team is very good, it may play another game after the season ends. The best teams play again on January 1, the first day of the New Year. Many people go to see these games and many others watch them on TV.

小题1:In American football players can_____.

A.only kick the ball

B.only throw the ball

C.only carry the ball

D.kick, throw and carry the ball小题2:Which is the best title for the passage?

A.American Football

B.Most People Like Football

C.Many People Enjoy Watching Football Games

D.American Football Is Not Like Soccer

填空题