问题 问答题

已知锌板的极限波长λ0=372nm.今用处于n=2激发态的氢原子发出的光照射锌板,已知氢原子能级公式En=

1
n2
E1,E1=-13.6eV,电子质量me=9.1×10-31kg,问:

(1)氢原子发出光子的能量多大;

(2)锌板发生光电效应时,光电子的最大初动能是多少;

(3)具有最大初动能的电子对应的德布罗意波长多大.

答案

(1)氢原子n=2能级的能量值 E2=

1
4
E1=-3.4eV,n=2激发态的氢原子跃迁到基态发出光子的能量 hν=E2-E1=-3.4eV-(-13.6eV)=10.2eV=1.632×10-18J.

(2)锌板的逸出功 W=hγ0=

hc
λ0
=
6.63×10-34×3×108
3.72×10-7
J=5.35×10-19J

由光电效应方程 Ek=hν-W=1.632×10-18J-5.35×10-19J=1.097×10-18J.

(3)由动能与动量的关系Ek=

p2
2m
,得电子动量

pe=

2meEk
=
2×9.1×10-31×1.097×10-18
kg•m/s=1.41×10-24kg•m/s

由德布罗意关系λ=

h
pe
得:λ=
6.63×10-34
1.41×10-24
m=4.7×10-10m.

答:

(1)氢原子发出光子的能量为1.632×10-18J.

(2)锌板发生光电效应时,光电子的最大初动能是1.097×10-18J.

(3)具有最大初动能的电子对应的德布罗意波长为4.7×10-10m.

阅读理解

阅读理解。

     The first American Thanksgiving Day celebration goes back to 1621. In that year, a special dinner was

prepared in Plymouth, Massachusetts. The people who settled there had left England because they were

forbidden to keep their religious belief. They came to the new land and faced difficulties in sailing across the

ocean. The ship which carried them was called "the May Flower". The North Atlantic was hard to travel.

There were bad storms and huge waves. With the help of the Indians, they learned to live on the new land.

These Puritans, as they were, enjoyed religious freedom. They learned how to grow their crops in accordance

with the climate and soil. Now when they selected the fourth Thursday of November for their Thanksgiving

celebration, they invited their neighbours, the Indians, to join them in dinner. They also wanted to pray God

for the new life. They recalled the group of 102 men, women and children who left England. They remembered

those who did not live to see the shores of Massachusetts. They thought of the 65 days' journey which tested

their strength.

1. The first celebration of the day of Thanksgiving is nearly _____ years old. [ ]

A.100

B. 200

C. 300

D. 400

2. Why had they left England? [ ]

A. To seek religious freedom.

B. To set up a new religion.

C. To learn new farming.

D. To live on the new land.

3. The climate and soil in Massachusetts were _____.  [ ]

A. similar to that of England

B. different from that of England

C. similar to that of Plymouth

D. different from that of Plymouth

4. They had their Thanksgiving celebration to remember _____. [ ]

A. the new society of Indians

B. their friends who died on the way to the new land

C. their former religion

D. their invitation to the Indians

5. How long did the trip last? [ ]

A. Six weeks.

B. Two months or more.

C. Half a year.

D. More than 200 days.

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