问题 问答题

现有一电池,其电动势E约为9V,内阻r在35~55Ω范围内,最大允许电流为50mA.为测定这个电池的电动势和内阻,某同学利用如图甲所示的电路进行实验.图中电压表的内电阻很大,对电路的影响可以不计;R为电阻箱,阻值范围为0~9 999Ω;R0为保护电阻.

(1)实验室备有的定值电阻R0有以下几种规格,本实验应选用______

A.10Ω,2.5W       B.50Ω,1.0W       C.150Ω,1.0W     D.1 500Ω,5.0W

(2)按照图甲所示的电路图,将图乙的实物连接成实验电路;

(3)该同学接好电路后,闭合开关S,调整电阻箱的阻值读出电压表的示数U,再改变电阻箱阻值,取得多组数据,然后通过作出有关物理量的线性图象,求得电源的电动势E和内阻r.

a.请写出与你所作线性图象对应的函数表达式______;

b.请在图丙的虚线框内坐标中作出定性图象(要求标明两个坐标轴所表示的物理量,用符号表示);

c.图丙中______表示E,______表示r.

答案

(1)当电阻箱的电阻调为零时,电路中电流最大,根据闭合电路欧姆定律得,电路中的最大电流为:

Im=

E
R0+r
,由此解得:R0=
E
Im
-r

由于内阻r在35~55Ω,代入解得R0的范围为:125Ω~145Ω.,故ABD错误,C正确.

故选C.

(2)根据原理图可得出实物图如下所示:

(3)根据闭合电路欧姆定律有:E=U+

U
R0+R
r,在进行数学变换时,注意变量为U何R,因此可以有以下两种不同的转换:

法一:

a.

1
U
=
r
E
1
R0+R
+
1
E

b.如图(法一)

c.纵轴截距的倒数,斜率除以纵轴的截距;

法二:

a.

1
R0+R
=
E
r
1
U
-
1
r

b.如图

c.斜率除以纵轴截距的绝对值,纵轴截距的倒数的绝对值;

故答案为:a、

1
U
=
r
E
1
R0+R
+
1
E
(或者
1
R0+R
=
E
r
1
U
-
1
r
);b、纵轴截距的倒数(或者:斜率除以纵轴截距的绝对值),c、斜率除以纵轴的截距(或者:纵轴截距的倒数的绝对值).

单项选择题
阅读理解

阅读理解。

     He wanted to go to college, and the only thing that might have stopped him was his disability.

     But this year, Zhang Yan and other physically disabled kids can realize their dream just like any other

students.

     As registration (报名) for this year's college entrance examinations draws near, the government has

loosened its requirements on physical examinations for new college students.

      A new rule was jointly decided in March by the Ministry of Education, the Ministry of Health and the

China Disabled Persons' Federation. It clearly states that no student should be rejected (拒绝) simply because

they have a physical disability.

      Schools may still advise disabled students on the choice of their major if it is likely to affect their future

chances of employment . However ,the final decision will be up to the student., 

     "Now I can just go ahead and do my best in the exams. I don't have to worry that my healthier classmates

will have the upper hand because of my disability," said Zhang happily.

     The 18-year-old boy will graduate this year from a Chengdu high school in Sichuan Province .He lost an

eye during an accident as a child.

      Zhang's mother called Peking University to ask if her son's eye problem would make it difficult for him to

accepted by the university's Bio-chemistry Department. She was happy to find out that their choice of students would be based "fairly" on exam results. 

     "The university official said my son would be judged at the same level as other students ,” said Zhang's

mother.

1. From the report we can infer that Zhang Yan probably _____.

A. is not sure of his success in the coming exam

B. does a very good job in his studies.

C. will not be chosen by the Peking University.

D. shows not much interest in Peking University.

2. From the 5th paragraph we can infer that ___.

A. some colleges have strict limits to disabled students

B. a major is not important to disabled students.

C. students are not free to choose their major.

D. students may have difficulty finding a job if their major is not chosen properly.

3. Which of the following statements is WRONG according to the report?

A. There will be no physical examinations for new college students this year.

B. Zhang Yan has some interest in Bio-chemistry.

C. Examination marks are quite important to students.

D. Many colleges used to set limits to disabled students.

4. Which can be the best headline for this report?

A. Zhang Yan Will Go To University.

B. Colleges Open Up To The Disabled

C.  Lucky Disabled Students

D. A New Rule For Colleges.