问题 问答题

如图所示,两根平行的光滑金属导轨与水平面成53°放置,导轨间接一阻值为3Ω的定值电阻R,导轨电阻忽略不计,在水平虚线L1、L2间有一与导轨所在平面垂直的匀强磁场B,磁场区域的宽度为d=1.0m.导体棒a的质量ma=0.2kg,电阻Ra=6Ω,导体棒b的质量mb=0.1kg,电阻Rb=3Ω,它们分别从图中M、N处同时由静止开始在导轨上无摩擦向下滑动,当b刚穿出磁场时,a正好进入磁场,且都是匀速穿过磁场区域,取重力加速度g=10m/s2,sin53°=0.8,cos53°=0.6,不计a、b之间电流的相互作用,求

(1)从导体棒a、b向下滑动起到a棒刚穿出磁场止,这个过程中,a、b两棒克服安培力分别做多少功?

(2)在a棒穿越磁场的过程中,a、b两导体棒中的电流之比是多大?

(3)M点和N点距L1的距离分别多大?

(4)在第(1)问的过程中,导体棒b上消耗的电能?

答案

(1)Fa=magsin53°

Wa=magsin53°×d=1.6J

同理:Wb=mbgsin53°×d=0.8J

(2)在a穿越磁场的过程中,a是电源,b是外电阻,b棒的电阻等于定值电阻,所以:

Ia
Ib
=
2
1

(3)设b在磁场中匀速运动时速度为vbI b=

BLvb
R总1

B2L2vb
R总1
=mbgsin53°

同理:

B2L2va
R总2
=magsin53°

R总1=5Ω,R总2=7.5Ω

va=vb+gsin53°×t,d=vb×t

因为sa=

va2
2gsin53°
sb=
vb2
2gsin53°

解得:sa=

9
4
m       sb=
1
4
m

(4)当b在磁场中匀速运动时Qb:QR:Qa=9:4:2,得Qb=0.8×

9
15
J=0.48J

当a在磁场中匀速运动时Qb:QR:Qa=1:1:8,得Qb=1.6×

1
10
J=0.16J

∴Q=0.64J

答:(1)从导体棒a、b向下滑动起到a棒刚穿出磁场止,这个过程中,a、b两棒克服安培力分别做功为1.6J、0.8J.

(2)a、b两导体棒中的电流之比是2:1.

(3)M点和N点距L1的距离分别为

9
4
m,
1
4
m.

(4)第(1)问的过程中,导体棒b上消耗的电能为0.64J.

阅读理解
Have you ever wondered: What drives successful people? Take a look around and talk to your friends and seniors who are very successful, you will see all of them have adopted certain values which have proved vital for their success.
It is evident that successful people take initiative (主动性). When they find something needs to be done, they just do it instead of waiting. They believe that responsibility is taken, not given. They weigh immediately what has to be done and then do it with pleasure, thus strengthening their reputation.
Successful people are enthusiastic about the things they do, especially when they believe in what they are doing. They are motivated by their own satisfaction and the joy they get from doing their work. They work hard even when no one is watching and they throw themselves into their work.
They do not fear failure. Failures and disappointments in life are unavoidable. It is failure that teaches us much more than success. Successful people pick themselves up after a fall and try again with more determination and commitment and learn from each failure. They associate with those they can learn from and enjoy the company of those who appreciate their achievement.
Having good IQ often gets a person what he wants but it’s really the EQ that keeps him there and helps him enjoy a high reputation. Successful people are polite to everyone and treat others with respect. By giving respect to others, they command respect for themselves.
Another important quality of successful persons is that they never complain. It’s better to praise others and win favor with them. So instead of complaining about a situation, successful people always try to solve it.
To put it shortly, take initiative and be enthusiastic about them. Do not be afraid to fail, but get up and start again. When you do so, success will be just around the corner.
Title: What Makes People Successful?
Brief introduction
Successful people all have adopted certain values which are(1)__________ for their success.
(2)_________
of successful people
Taking initiative
◆They take immediate action without hesitation.
◆They take responsibility for what has to be done and do it(3)__________.
Being self-motivated
◆They’re enthusiastic about the things they do with a(4)_______ in what they are doing.
◆They devote themselves to their work.
(5)__________ from failure
◆They get up and start again after a failure.
◆They keep company of those (6)__________ their achievement.
Giving respect to others
◆They are polite to everyone and treat others respectfully.
◆They earn respect in (7)_________ by giving respect to others.
Making no(8)________
◆They praise others and win favor with them.
◆They always try to find any possible    (9)__________ to the difficult situation.
Summary
When you can combine the above into your action plan, you’ll have    (10)___________ to success soon.
名词解释