问题 单项选择题 B型题

根据沉降公式(Stocks方程)计算所得的直径称为()

A.定方向径

B.等价径

C.体积等价径

D.有效径

E.筛分径

答案

参考答案:D

解析:

本组题考查粉体粒子大小的表示方法。 粒子大小的常用表示方法有:(1)定方向径:即在显微镜下按同一方向测得的粒子径。(2)等价径:即粒子的外接圆的直径。(3)体积等价径:即与粒子的体积相同球体的直径,可用库尔特计数器测得。(4)有效径:即根据沉降公式(Stocks方程)计算所得的直径,因此又称Stocks径。(5)筛分径:即用筛分法测得的直径,一般用粗细筛孔直径的算术或几何平均值来表示。

阅读理解

阅读理解。

     Last year my sixth-grader daughter, Elizabeth, was forced to put up with science. Her education week after

week, contained mindless memorization of big words like "batholith" and "saprophyte" She learned by heart the

achievements of famous scientists who did things like "improved nuclear fu-sion (核聚变)"-never mind that

she hasn't the least idea of what nuclear fusion means. Eliza-beth did very well (she's good at memorizing things ). And now she hates science. My eighth-grad-er son,Ben,also suffered from science education. Week after

week he had to perform lab experiments with answers already known.Ben figured out how to guess the right

answers, so he got good grades. Now he hates science, too.

     Science can provide an exciting way to develop children's curiosity. Science education should teach ways

to ask questions and week answers. But my children got the mistaken idea in school than science is difficult

dull and has no relation to their everyday interests.

     As a physicist, I am saddened and angered to see "the great science turnoff" I know that science is

important in our lives.Yet studies prove that our schools are turning out millions of graduates who know

almost nothing about and have almost no interest in science. What's gone wrong? Who is to blame?

1. We learn from paragraph 1 that _____.

A. the writer was proud of Elizabeth and Ben

B. both Elizabeth and Ben could become scientists

C. Elizabeth had to learn much about great scientists

D. Ben was good at trying new ideas in lab experiments

2. The writer thinks that in science education we should first _____.

A. get students interested in the subject

B. answer students' questions in delightful ways.

C. smooth out difficulties in lab experiments

D. explain the special terms clearly

3. By writing the text,the author questions _____.

A. the difficulty level of the science texts

B. the way science is taught in school

C. the achievements of famous scientists

D. students' poor records in science classes

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