问题 问答题

.1916年,爱因斯坦指出,光子不仅具有能量,而且像实物粒子一样具有大小为的动量.类H原子能级可用如下公式来描述:

,其中Z为原子序数.

(1) H原子基态和第一激发态的能量各为多少电子伏特?

(2)为使处于基态H原子进入激发态,入射光子所需的最小能量为多少?

(3) H原子从第一激发态跃迁回基态时,如果考虑到原子的反冲,辐射光子的频率与不考虑原子的反冲相比,是增大还是减小?求它所发射的光子波长的相对变化

(已知电子电荷取1. 60×10-19C,质子和中子质量均取1. 67×10-27kg,计算中可采用合理的近似)

 

答案

(1)-3.4eV

(2)10.2eV   (3)减小

:(1)类H原子能级表达式为,其中Z=1

基态和第一激发态分别对应n=l,n=2.则

基态 

第一激发态 

(2)使H原子进入第一激发态的入射光子最小能量为

(3)减小.

不计H原子反冲时,辐射的光子频率为

考虑H原子反冲时,设反冲的动能为,辐射的

光子为,由能量守恒得

可见辐射光子的频率降低了,能量减小了.

由动量守恒得,

波长的相对变化为

         

因为>>h>>h() 

所以 

阅读理解

Group buying is one of the fastest growing trends in South Africa today. Industry leaders are confident the growth potential remains strong since group buying is location-specific. Start-up costs are low and profit room remains high, so many sites continue to receive invested money despite widespread criticism and Facebook’s decision to phase out of deal business due to privacy concerns.

In the early stages of all industries, some companied fail because they cannot compete with stronger companies in difficult economic conditions. To deal with difficult conditions, an alarming number of businesses are developing group buying websites in places like China and India, so the increase of group buying in South Africa is nothing more than a natural progression into the international mainstream.

The group buying concept is fairly new and consumers have accepted this concept because they can now make full use of the rich information available on the Internet. Group buying is convenient and easy so it works. Anyone can view a site, join a mailing list, subscribe to RSS or print out a coupon(优惠券). The current group buying structure offered by the industry leaders works although there are still challenges to overcome.

Perhaps, the future of group buying is tied to the joining together of social media and mobile devices. Mobile devices are with us wherever we go and almost everyone is using some type of social media site like Facebook or Twitter to stay informed. Using GPS and social media technology to provide real time location-specific promotions would be beneficial to every consumer looking for the best deals in town.

Pause for a moment and think about it! What is better than signing on to your phone while having fun in town and you receive a real time information that your favorite shop across the street is offering a killer dial?

The future of the group buying in South Africa is bright and we can expect to see more advanced approaches to this concept in the future. In addition to the technological advances consumers will see the range of promotions expand to include new products and services.

小题1:What does the underlined phrase “phase out of” mean in the passage?

A.Gradually stop

B.Gradually increase

C.Begin to develop

D.Continue to enlarge小题2:The author sets China and India as examples to show that      .

A.China and India are powerful countries

B.China and India are in difficult economic conditions

C.group buying is successful worldwide

D.group buying is an international trend小题3: Which of the following is true according to the passage?

A.People have accepted group buying because it’s a new concept

B.Social media and mobile devices have been joined

C.GPS and social media technology will be helpful in group buying

D.Shops usually offer a killer deal when their customers are having fun小题4:The author’s attitude towards the future of group buying is     .

A.pessimistic

B.optimistic

C.objective

D.subjective小题5:What does the passage mainly tell us?

A.The history of group buying

B.Group buying in South Africa

C.The feature of group buying

D.The group buying concept

单项选择题