题干

学习了第七章《粒子与宇宙》后,我们知道组成物体的分子很小,肉眼是看不见的,那么我们如何通过身边的器材来估测下分子的直径呢?在这里,我们来学习下用油膜法来估测分子的直径.实验步骤和原理如下:

(1)实验的研究对象是油酸分子,我们在实验前可以通过注射器测量出每一滴油滴的体积为7.5×10﹣6cm3.

(2)把l滴该溶液滴入盛水的浅盘里,待水面稳定后,将玻璃板放在浅盘上,在玻璃板上描出油膜的轮廓.随后把玻璃板放在坐标纸上,其形状如图1所示.坐标纸中正方形方格的边长为2cm.我们可以数出轮廓内的方格数(格子未满半个的不计入各数,超过半个的算一格)

从而估测出这个油膜的面积是____ cm2.

(3)假设这层油膜是按如图2所示,由每个油酸分子紧密排列二组成的,则我们就可以估测出油膜分子的直径大约为____ cm.

上一题 下一题 0.0难度 选择题 更新时间:2017-09-16 11:54:53

答案(点此获取答案解析)

228,3.3×10﹣8

同类题2

阅读下面短文,完成已给了首字母的单词,使短文完整、通顺。

    An idiom is a phrase that we can't understand from the m____ of each word. For example, if an American boy asks his mom what's for dinner tomorrow, she may say “I'll play it by ear”, that means she doesn't have plans for dinner and she will d____ later.

    “Play it by ear” used to mean playing music w____ using the sheet music (乐谱), but now people often use it when they're not talking about music!

    There are many idioms in English. If you learn to use them, your English will be much more vivid (生动的) and colorful.

    Have you ever heard the idiom “He bought the farm”? It means he died. Do you know how it became p____? It was first used in World War I. When a soldier died, the government gave his family enough money to buy a farm.

    In the early 1930s, people in the US often didn't know when or where their next meal was. So once they got something in their hand that could be e____, it would go into their mouth. That was how people began to use the idiom “living hand to mouth” to mean “living a p____ life”.

    And don't be a____ if your English friend says this to you, “Break a leg in your game!” He is wishing you good luck! Hundreds of years ago, people believed in sprites (小妖精). Sprites enjoyed causing t____. If the sprites heard you ask for something, they would make the o____ happen. Tell someone to “break a leg” and the sprites would make something good happen.

    Aren't English idioms interesting? And break a leg in your next football m____!