问题 多选题

带电粒子进入云室会使云室中的气体电离,从而显示其运动轨迹,图是在有匀强磁场的云室中观察到的粒子的轨迹,a和b是轨迹上的两点,匀强磁场B垂直纸面向里.该粒子在运动时,其质量和电荷量不变,而动能逐渐减少.下列说法正确的是(  )

A.粒子先经过a点,再经过b点

B.粒子先经过b点,再经过a点

C.粒子带负电

D.粒子带正电

答案

粒子在云室中运动时,速度逐渐减小,根据r=

mv
qB
可知其运动轨迹的半径逐渐减小,故粒子运动方向为由a到b,故A正确,B错误;

运动方向由a到b,磁场垂直纸面向里,所受洛伦兹力方向指向运动轨迹内侧,故由左手定则可知该电荷带负电,故C正确,D错误.

故选AC.

多项选择题
阅读理解

 
A. What are SIGs?
B. What types of memberships are available?
C. Who can join IATEFL China?
D. What and where is IATEFL China?
E. What links does IATEFL China have?
F. What happens at the Annual Conference?
小题1:
 
IATEFL China is the International Association of English Language Teachers of English as a Foreign Language, China Branch. Its mother organization IATEFL was founded in the UK in 1967; it now has over 3,500 members in more than 100 countries throughout the world.
IATEFL China core activities are managed by the Secretariat headed by the President. The others include, Volunteer activities, SIG Coordinators, and the Publication Committee.
It is based in Tonghua City, Jilin Province of the People’s Republic of China and is managed by the President of the association. Other office staff include the General Secretary, the International Affairs Administrator, the Membership Secretary, the Newsletter Distribution, and the General Assistant.
小题2:
 
You can join as a full member and receive the association’s newsletter six times per year, two free publications, free membership to one SIG (Special Interest Group), discounts on publications, reduced conference registration fees, and voting rights.
There are also special membership packages for institutional members and for members of IATEFL China’s associates (basic members).
By the end of this year, members of IATEFL China can benefit from the special rights provided by the mother organization (IATEFL) at some rate.
小题3:
 
This is the most important event in the association’s calendar and takes place each year in August somewhere in China. It is attended by around 800 delegates each year and includes plenary sessions by eminent practitioners, a large number of workshops, talks and round table discussions given by able speakers, as ELT Exhibition and Pre-Conference Events organized by Special Interest Groups.
小题4:
 
Members can join any number of the 10 Special Interest Groups (SIGs) including: FLT Teaching & Learning Policy; FLT Curriculum & Syllabus Study; Coherence Research on Primary-secondary School and Secondary-Tertiary Transition; Primary School Classroom Instruction Model; Secondary School Classroom Instruction Model; Modern IT in FLT; Applied Linquistics; FL Learning Strategies; FL Teacher Development and Training; FL Textbook, Materials and Teaching Aids Design.
小题5:
 
IATEFL China has associate agreements with other teachers’ associations throughout the world. Among other things, there are usual agreements to exchange newsletters and to provide a speaker to attend each other’s conference at least once every year. More so, committee members from IATEFL China are willing to attend the conferences, meetings, etc. of related associations upon invitation.