文档介绍：of rural drinking water sources, protection of drinking water sources in rural areas by the end of the delimitation of t举例:如用过滤法除去食盐水中少量的泥沙。
13题，V2测的是电源电压，不变。又是这种两个电阻串联，一个电阻不变，另一个电阻变化，判断电压的题型，一定要会做了！滑片右移，电阻变大，那么滑动变阻器两端电压变大，V1变大。由于总电阻变大，那么串联电路的电流变小，A变小。
15题，实心木球和实心铁球的体积相等，木球放水中，铁球放酒精中。首先，ρ物<ρ液，物体漂浮，ρ物>ρ液，物体沉底。ABCD选项中，都是ρ
of rural drinking water sources, protection of drinking water sources in rural areas by the end of the delimitation of the scope of protection, complete with warning signs, isolating network protection facilities
of rural drinking water sources, protection of drinking water sources in rural areas by the end of the delimitation of the scope of protection, complete with warning signs, isolating network protection facilities
of rural drinking water sources, protection of drinking water sources in rural areas by the end of the delimitation of the scope of protection, complete with warning signs, isolating network protection facilities
木<ρ水，那么木球在水中漂浮，ρ铁>ρ酒精，铁球在酒精中沉底。木块漂浮，那么F浮木=G木=ρ木gV木，铁球沉底，F浮铁=ρ酒精gV铁〔因为沉底时V排=V铁〕
F1=ρ木gV木 F2=ρ酒精gV铁 而V木与V铁相等，所以
当ρ木 >ρ酒精时，F1 > F2;
当ρ木<ρ酒精时，F1 < F2。
16〔1〕蒸发，水汽输送
氧气
A
淘米水洗菜等
17 产生静电，负
18〔1〕神经元或者神经细胞 轴突
〔2〕1-2-3-4-5 AC
19〔1〕电流表示数
AB 〔3〕导体材料
20 〔1〕152364
〔2〕过滤时没有用玻璃棒引流
of rural drinking water sources, protection of drinking water sources in rural areas by the end of the delimitation of t