问题 问答题

某同学测量一只未知阻值的电阻.

(1)他先用多用电表进行测量,按照正确的步骤操作后,测量的结果如图(甲)所示.请你读出其阻值大小为______.为了使多用电表测量的结果更准确,该同学接着应该进行哪些操作?

答:

a.将选择开关打到“______”挡;

b.将两表笔短接,进行______;

c.再将被电阻接到两表笔之间测量其阻值并读出读数;

d.测量完毕将选择开关打到______.

(2)若该同学再用“伏安法”测量该电阻,所用器材如图(乙)所示,其中电压表内阻约为5kΩ,电流表内阻约为5Ω,变阻器阻值为50Ω.图中部分连线已经连接好,为了尽可能准确地测量电阻,请你完成其余的连线.

(3)该同学按照“伏安法”测量电阻的要求连接好图乙电路后,测得的电阻值将______(填“大于”、“小于”或“等于”)被测电阻的实际阻值.

答案

(1)由图甲可知,欧姆表示数是100×10Ω=1000Ω;

由图甲可知,欧姆表指针偏角太小,所选择的档位太小,为准确测量,应换大挡;

因此:应将选择开关打到“×100”挡;将两表笔短接,进行欧姆挡调零;

再将被电阻接到两表笔之间测量其阻值并读出读数;

测量完毕将选择开关打到“OFF”挡或交流电压最高挡.

(2)为准确测量,滑动变阻器应采用分压接法;

RV
R
=
5000Ω
1000Ω
=5,

R
RA
=
1000Ω
=200,
R
RA
RV
R
,因此电流表应采用内接法,电路图如图所示.

(3)由于电流表采用内接法,由于电流表的分压作用,使电压的测量值大于待测电阻上的实际电压,

从而使电阻测量值大于真实值,结果偏大.

故答案为:(1)1000Ω;×100;欧姆调零;“OFF”挡或交流电压最高挡;

(2)电路图如图所示;(3)大于.

阅读理解

This is the SCIENCE IN THE NEWS, I’m Barbara Klein.

Animal experts say one of the world’s most beautiful and rare kinds of big cat is close to disappearing from the wild. A study earlier this year found that about thirty Amur leopards(豹) still live free. The cats are also called Far Eastern leopards.

Recently, their numbers have been reduced by one. Some person shot a female Amur, then beat her to death. The animal’s body was discovered last month in the Barsovy National Wildlife Refuge in eastern Russia.

An official of the World Wildlife Fund, Darron, said this was the third such killing in the area in the past fives years. Mr. Collins said the death of even one adult female is a huge loss for the endangered cat. He noted that the killing reduces the possibility for cubs(幼兽) or young.

It is not clear how many Amur leopards still live free. One population count was performed in February and March. Wildlife expert Dmitry Pikuuov led this study. It found evidence of seven to nine males. The study identified(确定) three to seven females without cubs. Four leopards were identified as females with cubs. In all, five or six cubs were recorded. Six to eight animals could not be identified.

Most of the land where the Amur leopard once lived was in China. New roads and climate change there threatened(威胁) the animals. So did hunters who kill big cats for their body parts.

Mr. Pikuuov says adult Amurs need about five hundred square kilometers with good forests to survive. He said they also need a large and continuing supply of animals like deer for food. He believes the answer to saving the Amur leopard is for governments to provide protected spaces for wildlife.

小题1:This passage is probably from____________.

A.a magazine

B.a newspaper report

C.a TV report

D.a film小题2:Why is the killing of an adult female a huge loss?

A.It could lead to the death of an adult male.

B.It means it can not give birth to the young any more.

C.It is worth more money than a male.

D.There is only one adult female in the world.小题3:The number of the Amur leopards in China is becoming smaller because of all the following EXCEPT

A.new roads

B.climate change

C.human hunting

D.rare diseases小题4:According to the experts the Amur leopards ____________.

A.are living on plants

B.are living in the zoo

C.are well protected by people

D.are endangered

单项选择题