AP物理电场
1. C. Electric field is a vector. Look at the field at the center due to each charge. The field due to the left-hand charge points away from the positive charge; i.e., to the right; the field due to the right-hand charge points to the left. Because the charges are equal and are the same distance from the center point, the fields due to each charge have equal magnitudes. So the electric field vectors cancel! E = 0.
2. D. Electric potential is a scalar. Look at the poten-tial at the center due to each charge:
Each charge isdistance a/2 from the center point, so the potentialdue to each is kQ/(a/2), which works out to 2kQ/a. The potentials due to both charges are positive, so add these potentials to get 4kQ/a.
3. B. If the potential difference between plates is, say, 100 V, then we could say that one plate is At +100 V and the other is at zero V. So the poten-tial must change at points in between the plates.The electric ?eld is uniform and equal to V/d (d is the distance between plates). Thus, the potential incr eases linearly between the plates, and A must have twice the potential as B.
4. A. The electric ?eld by de?nition is uniform between parallel plates. This means the ?eld must be the same everywhere inside the plates.
[AP补充]第一章 静电学和高斯定律 1.1 静电的现象和电荷
静电的现象是我们人类生活中非常熟悉的现象，小到你经常被金属门把手“电到”（特别是你穿尼龙化纤衣物的时候），甚至你在和别人握手的时候，也可能突然感觉有个小精灵在你们之间跳来跳去（注意你们家铺了地毯的情况下），往往给你们带来些意外的“惊吓”！大到电闪雷鸣：
图1- 1
中国古代称之为雷公电母，其实仍然是小小的静电荷在发挥作用。
物理学的奇妙，就是要把最大的和最小的，最奇特的和最常见的，发现他们居然是同一个原因在不同环境下展示的不同现象罢了！
所以，能够发现以上静电现象都是基于一种“电荷”概念的存在，这个人一定很伟大，这个人就是本杰明.富兰克林，美国的开国元勋之一。
AP物理电场 - Copy
