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        My color television has given me nothing but a headache. I was able to buy it a little over a year ago because I had my relatives give me money for my birthday instead of clothes that wouldn’t fit. I let a salesclerk fool me into buying a discontinued model. I realized this a day later, when I saw newspaper advertisements for the set at seventy-five dollars less than I had paid. The set worked so beautiful when I first got it home that I would keep it on until stations signed off for the night. Fortunately, I didn't get any channels showing all-night movies or I would never have gotten to bed.

       Then I started developing a problem with the set that involved static(静电) noise. For some reason, when certain shows switched into a commercial, a loud noise would sound for a few seconds. Gradually, this noise began to appear during a show, and to get rid of it, I had to change to another channel and then change it back. Sometimes this technique would not work, and I had to pick up the set and shake it to remove the sound. I actually began to build up my arm muscles(肌肉) shaking my set.

       When neither of these methods removed the static noise, I would sit helplessly and wait for the noise to go away. At last I ended up hitting the set with my first, and it stopped working altogether. My trip to the repair shop cost me $62, and the sit is working well now, but I keep expecting more trouble.


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光的散射与丁达尔效应

光通过光学性质不均匀的介质时出现偏离原来传播方向,而沿侧向传播的现象,称为光的散射.在暗室里,将一束经聚集后的光线投射到胶体系统上,在与入射光垂直的方向上,可观察到一条明亮的光路,这就是丁达尔效应.产生丁达尔效应的实质是光的散射.

表1  分散系对可见光的不同作用


溶液

胶体

浊液

光路示意图

对光的主要作用

透射

散射

反射或折射

当入射光的波长略大于分散相粒子的直径时就发生光的散射.可见光的波长在400~760nm的范围,略大于一般胶体粒子的直径(1~100nm),因此当可见光束投射于胶体时,就发生光的散射,产生丁达尔效应.

对于溶液,分散质分子或离子更小,对可见光的散射作用很微弱;而当可见光束通过浊液时,由于分散质的粒子直径大于入射光的波长,主要发生反射或折射现象.

回答下列问题:

(1)产生丁达尔效应的实质是____ 

(2)制备Fe(OH)3胶体,在小烧杯中加入20mL蒸馏水,加热至沸腾后,向沸水中滴入5~6滴饱和的____ 溶液,继续煮沸至液体呈红褐色即可.

(3)胶体区别于其他分散系的本质特征是____ (填序号).

a.胶体有丁达尔效应        b.胶体粒子可以透过滤纸

c.胶体的胶粒带有电荷      d.胶体粒子的直径在1~100nm之间

(4)CuSO4溶液无明显丁达尔效应的原因是____