首先要讲一个大家都会关注的消息 就是习题课的助教们都不见了 我在星期一和星期三到物理系 但我找不到他们 所以..... 这个星期请大家自己努力了 好了 我还是讲一下我自己的做法和见解 (老实说 只有讲起物理功课 大家才会想起我) 但...... 我上一次自己做的功课只有65分 从此我都会问助教........... 从86题开始吧 因为86题算是最简单的 And we shift to English Channel NOW!!! (Don't ask me to translat it, please) 86) We should draw a free body diagram frist. The forces acting on the microshpere are drag force, which is opposite the motion of the microshpere, weight and electric field force. Read those statments, we know that weight and drag force are downward force and electric field force is upward force. Form the question, the microshpere reach terminal speed. Obviously, electric field force equals to the sum of weight and drag force. It's just simple. OK. now use the equation: electric field force = drag force + weight However, we have one problem, the given radius of the microsphere is 5.5 X 10^7 metre. It's impossible as the answer of part (c) will be faster than light speed. I suppose the radius of the sphere is 5.5 * 10^-7 metre. Here is the equation: qE = 6 * pi * radius * Eta * velocity + g * mass of the shpere 50) In problem 50, we should frist calculate the electric field at the bead. It's simple. The answer is Ex = 2kq/(a^2 + x^2)^3/2 Fx = -2kq^2 / a^2 * x as -2kq^2 / a^2 is a constant, the bead experiences a linear restoring force. In part b, use part a answer to complete it. 20) This is the hardest problem, I cannot describe it by text. Maybe I can show you some equations I used. W = F delta S F = qE mean free path equation: Lambda = 1/(2^1/2 * Nv * pi * d^2) ideal gas law: PV = NkT (delta s = Lambda) OK, we shift back to chinese channel. 打英文真的会快很多 大概20分钟就可以了 ========================================================================== 其实有很多人都看见我的nickname 会觉得很奇怪 根本不想叫出口........ 好了 你们还是叫我Derek好了 其实我的前nickname是有由来的 从前在补习班工作 我带的一群国中生都很聪明 家里有钱 还要很帅 (天杀的 他们是出木杉吗?) 基本上要和他们斗智 所以我们通常会互想挖苦对方 (基本上 我对他们很好) 有一次 我出去影印回来的时候 不小心偷听到了一部分的对话 ".....我说他一定没有女朋友" (我不否认) "他的生活像是一个神父一样" (是吗?) "又把自己的钱买东西请我们吃" (不好吗?) "可能他喜欢我们" (没有 =.=|||) "对呀 可能他是变态的" (......... 无奈状态) "直接叫他做神父好了" (.........) "变态的神父吗?" "他还是学生 当神父之前要当..." "要当修士" (本人已死 有事烧纸) 结果 不到两个小时 整个补习班都是这样叫我 那个晚上8:00 "可以走了吗 Derek哥" "我今天心情不错" 我知道我本来的nickname不是太好 那麽叫我Derek好了 -- 我还有一件事要说 如果你有耐心看完整篇文章 你会发现这个 http://www.megaupload.com/?d=N3XU4780 我不会用系上的空间 =.=||| 抱歉 重申 我上次自己做的功课只有65分 -- Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That's relativity. --Albert Einstein --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 140.112.239.70 ※ 编辑: DerekB98126 来自: 140.112.239.70 (03/04 20:43) ※ 编辑: DerekB98126 来自: 140.112.239.70 (03/04 20:48)