问题 问答题

纳米技术现在已经广泛应用到社会生产、生活的各个方面.将激光束的宽度聚光到纳米级范围内,可以精确地修复人体损坏的器官.糖尿病引起视网膜病变是导致成年人失明的一个重要原因,利用聚光到纳米级的激光束进行治疗,90%的患者都可以避免失明的严重后果.一台功率为10W氩激光器,能发出波长λ=500nm的激光,用它“点焊”视网膜,每次“点焊”需要2×10-3J的能量,则每次“点焊”视网膜的时间是多少?在这段时间内发出的激光光子的数量是多少?

答案

(1)已知激光器的功率P=10W,每次“点焊”需要的能量E=2×10-3J,根据E=Pt得

每次“点焊”视网膜的时间是

t=

E
P
=
2×10-3
10
s=2×10-4s

(2)设每个光子的能量为E0,则E0=hγ=h

c
λ

在这段时间内发出的激光光子的数量n=

E
E0
=
hc
=
2×10-3×500×10-9
6.63×10-34×3×108
个≈5×1015

答:每次“点焊”视网膜的时间是2×10-4s.在这段时间内发出的激光光子的数量是5×1015个.

选择题
阅读理解

阅读理解。

     When I was a little girl, my mom would say, "Half the fun of doing anything is sharing it with others."

   1   Friends and mates allow us to enjoy our successes and our joys, comfort us in our hard moments,

and provide a mirror for us to learn more about ourselves. I've always looked at friends as the family we

choose. They enrich our lives. As Robert Louis Steven once said, "  2  "

     To be a good friend or partner, it's important to be a good listener. Hear what your friend or mate has

to say first rather than jump to conclusions or get defensive.   3   When they hear their words repeated

back to them, it can help them to realize what they said was not exactly what they meant to say. 

       4    You know the old golden rule,"Care for others the way you would like them to care for you." The

support of a friend during a tough time could make the difference between success and failure.

Encouragement and confidence are the gifts that can help change a person's life.

     Take care, though, with whom you choose to have close relationship, for they can have a great effect

on yourself-respect and life path. As someone once told me,"   5   They will either take you up or down."

A. I am afraid so.

B. It is quite true.

C. Friendship is the most important factor.

D. Sometimes it is useful to be their mirror.

E. A friend is a present which you give yourself.

F. The attitudes of your friends are like the buttons on a lift.

G. Patience, sympathy and understanding are also important qualities.