问题 选择题

如图所示,匀强电场E竖直向下,匀强磁场B垂直纸面向里.现有三个带有等量同种电荷的油滴a、b、c,若将它们分别置入该区域中,油滴a保持静止,油滴b向左水平匀速运动,油滴c向右水平匀速运动,不计空气阻力,比较三个油滴所受重力(   )

A.油滴a所受重力最大

B.油滴b所受重力最大

C.油滴c所受重力最大

D.三个油所受滴重力一样大

答案

答案:B

题目分析:a球受力平衡,有  ①

重力和电场力等值、反向、共线,故电场力向上,由于电场强度向下,故球带负电;

b球受力平衡,有   ②

c球受力平衡,有   ③

由此可知mb>ma>mc

点评:难度较小,注意粒子的速度为零时不受洛仑兹力作用,左手定则中四指指向正电荷定向移动方向

完形填空

The people below are all trying to choose which TV program to watch. After the description of these people, there is information about five TV programs A-E. Decide which program would be most suitable for the person mentioned in questions 1-5 and then mark the correct letter (A-E) on your answer sheet.

小题1:Although Rob lives a quiet life in a small village, that doesn’t stop him from wanting to find out about the latest scientific development.

小题2:Bella enjoys eating out but can’t afford to spend very much at the moment as she is saving for a holiday. She has never learnt how to cook, so now might be quite a good time to find out!

小题3:Dan is interested in taking wildlife photographs and enjoys the kind of program which gives him a chance to see a professional photographer at work.

小题4:Gina is a music teacher. Although she prefers classical music, she likes to follow the kind of music that interests the teenagers she teaches.

小题5:Ron’s wife is in hospital. He wants to finds a program suitable for his three-year-old son while he gets on with the housework and prepares a meal.

TODAYS TELEVISION PROGRAMME PREVIEW

A.TV1 7:20 p.m. Find out more about Australia’s animal life. This film was made last year by one of Australia’s best-known cameramen, Dougie Bond. He spent over 200 hours filming the birds, animals and fish that inhabit this beautiful continent and for the first time brings some of these unusual animals to our TV screens.

B.TV3 9:00p.m. The popular science program is back with the latest in technology and medicine. This week, cars that run on sunlight and the story of one baby’s fight to live.

C.TV1 5:15p.m. Busy parents? Bored children? Do you want something educational to entertain your children while you do something else? This popular magazine program is for the under-fives. More music, fun, songs and games with Carla and Larry.

D.TV3 8:45p.m. If you’ve always wanted to cook, now’s your chance to learn. In the studio are two chefs who will take you through some simple recipes step by step. This is a repeat of the popular series shown last year, and available from good bookshops.E. TV3 7:40p.m. The latest new music. Pete Hogg looks at the best of the current rap, raga and new jack swing plus new video releases. This is the program that tells you all about what’s happening on the music scene and brings you interviews with tomorrow’s young artists.

单项选择题