问题 选择题

某光电管的阴极为金属钾制成的,它的逸出功为2.21eV,如图是氢原子的能级图,一群处于n=4能级的氢原子向低能级跃迁时,辐射的光照射到该光电管的阴极上,这束光中能使金属钾发生光电效应的光谱线条数是(  )

A.2条

B.4条

C.5条

D.6条

答案

第四能级的氢原子可以放出6条光谱线,其放出的光子能量分别为:

E1=-0.85-(-1.51)=0.66eV;

E2=-0.85-(-3.40)=2.55eV;

E3=-0.85-(-13.6)=12.75eV;

E4=-1.51-(-3.40)=1.89eV;

E5=-1.51-(-13.6eV)=12.09eV;

E6=-3.40-(-13.6)=10.20eV;

故大于2.21eV的光谱线有4条;

故选B.

单项选择题
单项选择题

Low levels of literacy and numeracy have a damaging impact on almost every aspect of adults, according to a survey published yesterday, which offers (1) of a developing underclass. Tests and (2) with hundreds of people born in a week in 1958 graphically illustrated the (3) of educational underachievement. The effects can be seen in unemployment, family (4) , low incomes, depression and social inactivity.

Those who left school at 16 with poor basic skills had been employed for up to four years less than good readers (5) they reached 37. Professor John Bynner, of City University, who carried the research, said that today’s (6) teenagers would even encounter greater problems because the supply of (7) jobs had shrunk.

Almost one fifth of the 1,700 people interviewed for yesterday’s report had poor literacy and almost half (8) with innumeracy, a proportion (9) other surveys for the Basic Skills Agency. Some could not read a child’s book, and most found difficult (10) written instruction.

Poor readers were twice as likely to be a low wage and four times likely to live in a household where partners worked. Women in this (11) were five times as likely to be (12) depressed, (13) both tended to feel they had no control over their lives, and to trust others (14) .

Those who had low literacy and numeracy were seldom (15) in any community organization and less likely than others to (16) in a general election. There had been no (17) in the literary level of (18) reporting problems.

Alan Wells, the agency’s director, said: “ The results emphasize the dangers of developing an underclass people, who were out of work, (19) depressed and often labeled themselves as (20) . There is a circle of marginalization, with the dice against these people and their families.”

3()

A.defect

B.backwardness

C.handicap

D.scarcity