问题 多选题

如图所示,两个固定的相同细环相距一定的距离,同轴放置,O1、O2分别为两环的圆心,两环分别带有均匀分布的等量异种电荷.一带正电的粒子从很远处沿轴线飞来并穿过两环.则在带电粒子运动过程中(  )

A.在O1点粒子加速度方向向左

B.从O1到O2过程粒子电势能一直增加

C.轴线上O1点右侧存在一点,粒子在该点动能最小

D.轴线上O1点右侧、O2点左侧都存在场强为零的点,它们关于O1、O2连线中点对称

答案

A、在O1点时,右环上电荷由于关于O1对称,所以其在O1产生的电场强度为0,而-Q各点在O1产生的场强水平向左,故+q在O1点所受电场力方向向左,故加速度的方向水平向左,故A正确.

B、在+q从O1向O2运动的过程中+Q对+q的电场力向左,-Q对+q的作用力方向也向左,故电场力对+q始终做正功,故+q的电势能一直减小.故B错误.

C、根据E=

kQ
r2
可知在O1右侧+Q产生的场强的先增大后减小且一直减小到0,而-Q的场强大多数情况下小于+Q产生的电场但场强却不会为0,故合场强为0的位置应该在O1的右侧,而在合力为0之前合外力做负功,动能持续减小,之后合力做正功,动能增大,故动能最小的点在O1的右侧,故C正确.

D、根据E=

kQ
r2
可知在O1右侧+Q产生的场强的先增大后减小且一直减小到0,而-Q的场强大多数情况下小于+Q产生的电场但场强却不会为0,故合场强为0的位置应该在O1的右侧,同理O2的左侧也有场强为0的位置,而O1和O2之间场强始终大于0,由于两个电荷的电荷量相同,故电场关于O1、O2的连线对称,故D正确.

故选ACD.

选择题
阅读理解

Sports is not only physically challenging, but it can also mentally challenging. Criticism(批评)from coaches(trainers), parents, and other teammates, as well as pressure to win can create too much anxiety or stress for young athletes. Stress can be physical, emotional, or psychological, and research has showed that it can lead to burnout. Burnout has been described as dropping or quitting of an activity that was at one time enjoyable.

The early years of development are critical years for learning about oneself. The sport setting is one where valuable experiences can take place. Young athletes can, for example, learn how to cooperate with others, make friends, and gain other social skills that will be used throughout their lives. Coaches and parents should be aware(realize), at all times, that their feedback(反馈)to youngsters can greatly affect their children. Youngsters may take their parents’ and coaches’ criticisms to heart and find a flaw(缺陷) in themselves.

Coaches and parents should also be cautious(careful) that youth sport participation does not become work for children. The outcome of the game should not be more important than the process of learning the sport and other life lessons. In today’s youth sport setting, young athletes may be worrying more about who will win instead of enjoying themselves and the sport. Following a game, many parents and coaches focus on(pay more attention to) the outcome and find fault with youngsters’ performances. Positive reinforcement should be provided in spite of the outcome. Research shows that positive reinforcement motivates and has a greater effect on learning than criticism. Again, criticism can create high levels of stress(pressure), which can lead to burnout.

小题1:According to the passage sport is positive for young people in that       

A.it can help them learn more about society

B.it teaches them how to set realistic goals for themselves

C.it enables them to find flaws in themselves

D.it can provide them with valuable experiences小题2:According to the passage parents and coaches should       

A.help children to win every game

B.pay more attention to letting children enjoy sports

C.enable children to understand the positive aspect of sports

D.train children to deal with stress小题3:The author’s purpose in writing the passage is        

A.to persuade young children not to worry about criticism

B.to emphasize the importance of positive reinforcement to children

C.to discuss the skill of combing criticism with encouragement

D.to teach young athletes how to avoid burnout