问题 选择题

如图所示为氢原子的能级示意图,一群氢原子处于n=3的激发态,在向较低能级跃迁的过程中向外发出光子,用这些光照射逸出功为2.29eV的金属钠,下列说法中正确的是

A.这群氢原子只能发出三种频率不同的光,其中从n="3" 跃迁到n=2所发出的光波长最短

B.金属钠表面所发出的光电子的初动能最大值为9.80eV

C.金属钠表面所发出的光电子的初动能最大值为11.31eV

D.这群氢原子只能发出两种频率不同的光,其中从n=3跃迁到n=1所发出的光频率最高

答案

答案:B

分析:氢原子能级间跃迁时,吸收和辐射的光子能量等于两能级间的能级差,能级差越大,光子频率越大.根据光电效应方程求出光电子的最大初动能.

解答:解:一群氢原子处于n=3的激发态,可能发出3中不同频率的光子,因为n=3和n=1间能级差最大,所以从n=3跃迁到n=1发出的光子频率最高,波长最短.故A、D错误.

从n=3跃迁到n=1发出的光子频率最高,发出的光子能量为13.60-1.51eV=12.09eV.根据光电效应方程EKm=hv-W0得,最大初动能Ekm=12.09-2.29eV=9.80eV.故B正确,C错误.

故选B.

点评:解决本题的关键知道能级间跃迁辐射或吸收光子的能量等于两能级间的能级差,以及掌握光电效应方程EKm=hv-W0

阅读理解

第三部分阅读理解(共10小题;每小题2分,满分20分)

How many times have you laughed today? Have you ever wondered what makes you laugh? In the whole animal kingdom, only we humans are capable (有能力的) of laughter. On average, we laugh about 17 times a day.

Laughter is a spontaneous reaction of the body to some-thing funny or pleasant. Have you noticed that when you laugh, many parts of your body respond (反应)? Your face changes expression, your breathing changes, and muscles throughout your body are affected.

An interesting story dates back to 1962. In a school in Tanganyika, in Africa, a group of schoolgirls started laughing uncontrollably over a joke. This laughter became epidemic (传染的), jumping from one person to the next, spreading across communities, and lasting for six months! So strong was the "laughter epidemic" that schools had to shut down till it ended.

How we laugh remains a mystery. Whatever the reasons, laughter, as the saying goes, "is the best medicine." In fact, science has proven that being happy and laughing can not only keep us healthy and fit but help deal with serious illnesses.

Laughing exercises all the important muscles, and keeps you fit. People have started forming laughter clubs that use laughter to treat illnesses. They meet at specific places at fixed times and laugh together. Laughter spreads, so this exercise works best in groups; once one person starts laughing, others automatically (自动地) join in.

56. The underlined word "spontaneous" in the second paragraph probably means "______".

A. perfect            B. strange            C. natural         D. terrible

57. People have formed laughter clubs to ______.

A. kill time          B. relax         C. meet others        D. keep healthy

58. The best title for the passage would be ______.

A. A Laughter Epidemic

B. Laughter, What It Is, and What It Can Do

C. The Relationship Between Laughter and Health

D. How Laughter Helps Cure Disease

59. The passage is probably taken from a(n) ______.

A. ad         B. novel            C. magazine           D. medical book

判断题