首先要講一個大家都會關注的消息 就是習題課的助教們都不見了 我在星期一和星期三到物理系 但我找不到他們 所以..... 這個星期請大家自己努力了 好了 我還是講一下我自己的做法和見解 (老實說 只有講起物理功課 大家才會想起我) 但...... 我上一次自己做的功課只有65分 從此我都會問助教........... 從86題開始吧 因為86題算是最簡單的 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. 打英文真的會快很多 大概20分鐘就可以了 ========================================================================== 其實有很多人都看見我的nickname 會覺得很奇怪 根本不想叫出口........ 好了 你們還是叫我Derek好了 其實我的前nickname是有由來的 從前在補習班工作 我帶的一群國中生都很聰明 家裏有錢 還要很帥 (天殺的 他們是出木杉嗎?) 基本上要和他們鬥智 所以我們通常會互想挖苦對方 (基本上 我對他們很好) 有一次 我出去影印回來的時候 不小心偷聽到了一部分的對話 ".....我說他一定沒有女朋友" (我不否認) "他的生活像是一個神父一樣" (是嗎?) "又把自己的錢買東西請我們吃" (不好嗎?) "可能他喜歡我們" (沒有 =.=|||) "對呀 可能他是變態的" (......... 無奈狀態) "直接叫他做神父好了" (.........) "變態的神父嗎?" "他還是學生 當神父之前要當..." "要當修士" (本人已死 有事燒紙) 結果 不到兩個小時 整個補習班都是這樣叫我 那個晚上8:00 "可以走了嗎 Derek哥" "我今天心情不錯" 我知道我本來的nickname不是太好 那麼叫我Derek好了 -- 我還有一件事要說 如果你有耐心看完整篇文章 你會發現這個 http://www.megaupload.com/?d=N3XU4780 我不會用系上的空間 =.=||| 抱歉 重申 我上次自己做的功課只有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 --

※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 140.112.239.70 ※ 編輯: DerekB98126 來自: 140.112.239.70 (03/04 20:43) ※ 編輯: DerekB98126 來自: 140.112.239.70 (03/04 20:48)