问题 问答题

[物理-选修3-5]

(1)关于光电效应,下列说法正确的是______(填入选项前的字母,有填错的不得分)

A.极限频率越大的金属材料逸出功越大

B.只要光照射的时间足够长,任何金属都能产生光电效应

C.从金属表面出来的光电子的最大初动能越大,这种金属的逸出逸出功越小

D.入射光的光强一定时,频率越高,单位时间内逸出的光电子数

(2)两个质量分别为M1和M2的劈A和B,高度相同,放在光滑水平面上.A和B的倾斜面都是光滑曲面,曲面下端与水平相切,如图所示.一质量为m的物体块位于劈A的倾斜面上,距水平面的高度为h.物块从静止开始滑下,然后又滑上劈B.求物块在B上能够达到的是大高度.

答案

(1)A、根据W=hγc知,极限频率越大的金属材料逸出功越大.故A正确.

B、发生光电效应的条件是入射光的频率大于极限频率,与入射光照射的时间无关.故B错误.

C、根据光电效应方程Ek=hγ-W知,光电子的最大初动能与入射光的频率和逸出功两个因素有关,光电子的最大初动能越大,这种金属的逸出逸出功不一定越小,也可能是因为入射光的频率高的缘故.故C错误.

D、光的强度影响的是单位时间发出光电子数目,与入射光的强度无关.故D错误.

故选A

(2)设物块到达劈A的底端时,物块和A的速度大小分别为v和V,由机械能守恒和动量守恒得

mgh=

1
2
mv2+
1
2
M1V2

M1V-mv=0  ②

解得,v=

2M1gh
M1+m

设物块在劈B上达到的最大高度为H,此时物块和B的共同速度大小为V',对物块与B组成的系统,由机械能守恒和水平方向动量守恒得

  mgH+

1
2
(M2+m)V2=
1
2
mv2 ③

  mv=(M2+m)V'④

联立得 H=

M1M2h
(M1+m)(M2+m)

故答案为:(1)A

(2)物块在B上能够达到的是大高度为

M1M2h
(M1+m)(M2+m)

阅读理解

Every once in a while, it is necessary to take a step back in order to take a long, hard look at where we are in our lives. At this point, it is good to ask yourself a bunch of critical questions. Are you at the point in your career where you want to be ? Have you so far accomplished all of your goals in life ? If so, then maybe it is time to make goals that stretch yourself a bit more. If you have not accomplished your goals in life, then perhaps you have made the mistake of setting too many goals or trying to accomplish them at an unnaturally fast pace.

It is necessary to set reasonable, intelligent goals in order to succeed in life. Do not be unrealistic because life is not a fairy tale. But you should try to recognize what you want, and to be as specific as possible when attempting to visualize(形象化) or otherwise express what your goals in life are.

In order for a goal to sufficiently motivate you, it needs to be a major one. The bigger your goals are, then the more motivated you will need to be to work towards accomplishing them. If you want, for example, to be the greatest concert pianist, in the world, then you are going to find yourself a lot more motivated than you would be if your goal were merely to, say, play a couple of Beethoven pieces extremely well. If you are a beginner, then no doubt mastering those tough songs is a very intelligent and realistic goal to set. But if that is your only goal as a pianist, then you will stop growing as a pianist once that goal has been achieved. This is why it is necessary to constantly stop and re-evaluate our goals so that we are aware of what they are, and thus stay motivated.

小题1:From the passage, if your goals have all been achieved, you should then ______.

A.ask yourself some serious questions

B.take a hard look at your success

C.set some other intelligent goals

D.stretch yourself to relax小题2:By saying “life is not a fairy tale”, the author suggests that you should ________ .

A.set as big a goal as possible

B.try hard to realize your dream

C.make your goals practical

D.abandon all your ambitions小题3: To perform several Beethoven pieces well is a goal that _______.

A.is not suitable for the pianist

B.is appropriate for a beginner

C.stops you from growing as a pianist

D.is very easy to achieve小题4:What is the best title for the passage ?

A.Set Intelligent Goals for Yourself

B.Try to Accomplish Your Goals

C.Get Yourself More Motivated

D.Goals Help You to Succeed

单项选择题