物理

磁性流體（magnetic fluids）是一種含有磁性奈米粒子的液體，當磁場外加於磁性流體時，流體中各磁性奈米粒子的磁矩會沿外加磁場方向排列，而導致粒子間相互吸引，形成較大的磁性叢集，即所謂的磁鍊。當外加磁場增強，該磁鍊數會變多，並使磁性流體的折射率產生變化。磁性流體的折射率變化會隨外加磁場之變大而增大。本研究除探討磁性流體折射率受外加磁場控制的變化情形及其物理原由外，並進一步運用此特性研發可調性光纖「光調制器」 ，以探討磁性流體可調性折射率應用在光電元件上的可行性。A magnetic fluid is one kind of colloids which contain magnetic nano-particles. Under an external magnetic field, the magnetic moment of nano-particles is aligned along the direction of the external magnetic field. This leads to the agglomeration of magnetic particles and to form magnetic clusters under an external magnetic field. With the formation of the magnetic clusters, the refractive index of magnetic fluid is varied. The refractive index of magnetic fluid was found to increase under a higher magnetic field. In this work, In addition to investigating in detail the behavior of the field-dependent refractive index of the magnetic fluid, we also explore the relevant physical origins. Furthermore, the feasibility of developing fiber-optical modulators by utilizing the tunable refractive index of magnetic fluids is discussed.

雷射光碟（以下簡稱ＣＤ）除了在電腦、音響方面有甚佳的視聽功能外，在光線照射下，呈現彩虹狀的光譜，必定引起你我研究其光學性質的興趣。國內以ＣＤ研究光的繞射的著作，有李偉等四人近三年發表五篇，國外科教期刊自1991年迄今共有19 篇，在老師指導下，利用ＣＤ進行了8 項實驗，分成三大項。1.利用氦氖雷射分別照射舊唱片、ＣＤ、ＤＶＤ，反射光形成繞射現象，由dsinθ=mλ，量出槽距。2.將ＣＤ-R 的鋁層刮掉，（整疊購買的ＣＤ-Ｒ上下有數片未鍍鋁的瑕疵片），成為透光式ＣＤ（透射式光柵），將其中心半徑5.5 公分部份，用黑紙遮住，正對陽光，螺旋狀的溝槽將陽光聚成一點，量出各色光到ＣＤ的距離，可算出色光的波長。3.透射式ＣＤ置於投影機鏡頭前方，投影機置物台上，放置化學藥品，可直接在屏上觀察吸收光譜。The rainbow of colors reflected from the surface of an audio compact disc (CD) is a familiar sight.It is the phenomenon of light diffraction. A standard CD has 20,625 turns of the spiral, and each line is spaced by 1.6μm. This provides a grating of 625 lines/mm. We used ordinary CDs as reflection grating in our experiment,and transparent factory rejects with no coating but printed data spirals as diffraction grating. We conducted eight experiments of diffraction using the two kinds of CD. (a) Determined the grating spacing of an ordinary CD using a laser beam. (b) Determined the grating spacing of a transparent CD using a laser beam. (c) Studied the diffraction patterns caused by a laser beam held at angles to a transparent CD. (d) Measured the wavelengths of sunlight using a transparent CD. (e) Measured the wavelengths of sunlight using an ordinary CD. (f) Formed a rainbow using a transparent CD. (g) Observed the scattering of light using a transparent CD. (h) Demonstrated the absorption spectrum using a transparent CD and an overhead projector.

一般人從小就知道如果要判斷西瓜有無成熟，只要用手輕拍瓜皮，利用聲音的特性就可以知道西瓜是否成熟，此技術看起來容易，卻需有多年經驗之西瓜商始可為之。本研究利用拍擊西瓜所造成之聲音進行非破壞性音波檢測，來探討西瓜之成熟度。換言之，本研究希望在依照西瓜商拍擊的習慣下，從客觀的科學角度，探討存在於西瓜商手上「聽音辨瓜」的奧秘。由研究結果得知，西瓜的拍聲在頻譜中可分為三個頻區，即西瓜殼所造成的高頻區，水及含水量高的果肉所形成的中頻區，及由空洞及含水量低的果肉所造成的低頻區，而西瓜商就是藉由這三種音頻所表現出的綜合效果進行判斷。The method, tapping the watermelon rind and listening to the sound, has been often used to judge whether the watermelon is mature or not. Although it is not difficult to tap the rind of a watermelon, it is not so easy to have a correct judgment of the maturity just from the sound you heard, unless you are an experienced watermelon farmer. In order to investigate the secret that the farmers have, this research detects and analyzes the sound of tapping watermelons in an objectively scientific way. According to the experimental results, the sound could be approximately partitioned into three regions in the frequency spectrum, denoted as high-frequency, mid-frequency, and low-frequency regions. The high-frequency region and mid-frequency region are resulted from the hard solid rind and the juicy flesh of a watermelon, respectively. As for the low-frequency region, it comes from the vacant holes or flesh with little amount of water. Based on the experiment, it can be concluded that the maturity of a watermelon can be correctly judged from the combination of these three frequency regions, just like the farmer’s method.

本研究欲探討垂直水柱遇障礙物成節的形成機制。以數位照相機、光電計時器等進行觀測。 實驗結果如下： （一）因往返水柱波速不同，而且節無波腹大幅振動現象，故節不是駐波現象。 （二）細針插入水柱表面時，當針上方超過某長度後，針下方產生Ｖ字形震波。但不論針相對水柱的速度是否超過波速，針上方都有節，故不是震波所產生的現象。 （三）根據水波槽模擬實驗，不論木條是否超過波速，木條前方均產生波紋。木條前方的水受到木條推動，往前方加速，因此顯現出波紋了。 我們認為，在水柱中所看到的節，不是震波或駐波，而是相對於木條往前傳遞的波。波源是撞擊物，改變了水柱表面的壓力，而成為波源，水柱的水因受撞擊，某個範圍內流速會小於波速，使得撞擊物前方存在波紋。This experiment uses digital camera and photoelectric timer to discuss the mechanism of causing spouts to form nodes on its surface. Because the downward wave velocity of the spout is different from that upwardand there are no significant vibrations of antinodes, standing waves are not the mechanism of causing nodes. In the experiment of inserting a needle into the spout, we found out that while the needle was inserted above a certain length of the spout, v shaped bow waves emerged. However, no matter the velocity of the needle related to the spout is over the wave velocity, there are always nodes above the needle. Therefore, bow waves are not the mechanism of causing nodes. According to the ripple tank simulating experiment, no matter whether the speed of the wooden stick is faster than the wave velocity or not, there are always waves forming in front of the wooden stick. The wooden stick pushes water in front of it and causes the water to accelerate forward. Therefore, waves appear. We think that the nodes we see on spouts are neither standing waves nor bow waves. The nodes are rather caused by the relatively moving wooden stick. The object, which impacted the spout (wooden stick), changed the pressure of the spout’s surface and became the source of wave. Because of the impact, the velocity of the water current of a certain area became slower than the wave velocity and causes nodes forming on the surface of the spout.

密閉容器置入待測液，放入浮沉子，施加壓力，當浮沉子恰要沒入液中瞬間，因表面張力的總力達極大值且向上，外加壓力(p1)為極大值，浮沉子沒入液中；液面減壓，當浮沉子在液面正下方時，外加壓力 p2，量 p1、(p1- p2)，浮沉子的質量 m，外半徑 R，及玻璃管的體積 G V ，可求得液體表面張力。 液面再減壓，浮沉子恰要露出液面時，表面張力的總力達極大值且向下，外加壓力(p3)為極小值，量 p3、(p2- p3)，浮沈子的質量 m，外半徑 R及 G V ，應亦可求得表面張力；但實驗時浮沉子漂移到容器邊，並吸附在器壁上，因此發現浮沉子的”Cheerios effect”。 利用浮沉子和容器的相吸及相斥現象，可解釋西式早餐的小榖片放入牛奶中為何會漂移到碗緣，並支持 Vella在 2005 年 9 月份美國物理期刊(AJP)認為 Cheerios effect的成因除了由於接觸角不同外，浮力、重力、表面張力共同作用，使小榖片間有相吸、相斥現象。 The experiment apparatus is equipped with a Cartesian diver by using a glass tube with air trapped inside that floats or submerses in a closed vessel containing liquid. The external pressure may be varied with a syringe and measured with a water manometer. The maximum pressure P1 inside the vessel is measured when the diver is just about to sink, where the surface tension that acts on the diver is upward. Then the pressure P2 of the vessel is measured when the diver is just beneath the liquid surface, where no surface tension acts on the diver. Finally, the surface tension is calculated from P1, P2 and the radius of the diver, R. When the pressure inside the vessel is decreased, the diver will rise. As the diver is about to emerge from the liquid, we get the minimum pressure P3 inside the vessel, and the surface tension that acts on the diver is downward. By measuring P3, P2, and R, the magnitude of surface tension is found to be the same as above. When the diver is just about to sink into the liquid, it floats to the center of the vessel. When the diver is about to emerge from the liquid, it sticks to the wall of the vessel. This phenomenon is named the “Cheerios effect.” Our results again strongly support that the cause of the effect is due to the different contact angles between the diver and water, as well as the balance of gravity and surface tension in the case of the sinking diver, and the balance of buoyancy and surface tension in the case of rising diver as Vella claimed in his paper (AJP 73, 817 (2005)).

本實驗使用磁流變流體(Magnetorheological fluid, MRF)來估查其磁場作用下的光學性質。本實驗採用Lord公司的MRF-132LD磁流變流體加以稀釋到不同的重量濃度，並以氫氟酸蝕刻玻片產生不同的厚度。吾人觀察到濃度參數以及厚度參數均對MRF薄膜的光繞射產生影響。膜厚越薄，產生的繞射較明顯，而重量濃度較小的容易亦有較大的繞射角度。吾人亦移動上下兩玻片相對位置，施加剪力的作用，繞射現象也產生明顯的改變。\r The Magnetorheological fluid (MRF) is used to observe the optical properties under the vertical magnetic field , The MRF-132LD from Lord Company is used, The MRF is diluted to different weight ratio of particulate and carrier fluid . The different thicknesses of the MR thin film are also made with the diluted MRF. The concentration of the MRF and the thickness of the thin film are both found to have significant effects on the optical diffraction phenomenon. The optical diffraction is also found to be affected by the applied shear force to the thin film.

隨著社會漸漸的現代化，我們需要愈來愈多的電力，然而在享用電力時，更伴隨著汗染的到來。所以討論如何有效的利用能源及探討無汗染能源，是本實驗研究的主要課題，以下即是我們的介紹。

The purpose of the research is to investigate the settling mode of the viscid micro-particle, such as the ones from the “Miso Soup”, in static liquid. We constructed the “constant temperature environment” by constant temperature trough and transparent glass trough. The data is gathered from pictures captured from DV and then analyzed by Media Player. We did a stability test prior to the start of the experiment and found the system with good stability. The results of the experiment are as followed: 1. The settling mode can be divided into four phases: (a) Initial accelerated phase (b) Maximum phase (c) Gradually decelerated phase (d) Stationary phase. 2. The lower the fluid concentration is in the fixed temperature: a. the faster its settling interfaces appears; and the deeper it becomes for the depth of its settling interface. b. the faster the maximum sedimentation rates of the settling interface becomes and the slower it appears. 3. At the fixed concentration, the higher temperature: a. has the bigger maximum sedimentation rates of the settling interface b. gets to the stationary phase sooner c. has shallower stationary settling interfaces d. the time when the settling interface appears is independent with the temperature 4. The shape of the container has no effect on the settling mode as the settling interface is always perpendicular to gravity field. 5. If we add salt into the liquid, the stationary settling interfaces of the result will be higher than non-added ones.本研究的目的在於探討味噌這樣的微小黏性顆粒，在靜止液體中的沈澱模式。運用恆溫槽與透明玻璃水槽所建構之恆溫環境透過數位攝影機，以電腦播放軟體於特定時間擷取畫面進行分析。在正式實驗前，進行了穩定性試驗，發現穩定性良好。實驗的結果發現：一、 沈降模式：可以分為四個時期，分別為（一）起始加速期（二）高峰期（三）逐漸穩定期（四）完全靜止期。二、 在固定溫度下，溶液濃度越低：(一) 出現沈降交界面的時間越短且穩定距離距液面越深。(二) 沈降面沈降速率最大值越大且出現的越晚。三、 在固定濃度下，溶液溫度越高：(一) 沈降面沈降速率最大值越大。(二) 沈降交界面完全靜止期出現的時間越短，也就是越快達到穩定。(三) 沈降交界面的穩定距離距液面越淺。(四) 沈降面沈降速率最大值出現的時間與溶液的溫度無關。四、 容器內部的形狀與沈降面的沈降行為並沒有影響，都是成與重力場垂直的水平線沈降。五、 添加食鹽之後最終穩定沈降面比同濃度同溫度的高了許多。表示添加了食鹽對於味噌溶液有阻止沈澱的效果。

This experiment mainly aims at three kinds of solution - Dextrose, Saccharose, and Fructose. By changing its temperature, density, length of tube, as well as different wave length factor of polarized light, we observe the influence of the direction of polarization by those factors. The experimental result showed as follow. The Dextrose and the Saccharose can cause the polarized light with the rotary direction of clockwise, so both are ‘dextrorotatory’. The Fructose can cause the polarized light with the direction of counterclockwise, so it is the ‘laevorotatory’. For the Dextrose, when the\r temperature is lower than 20℃, the direction of polarization has changed observably, but doesn’t have any rule. When the temperature is higher than 20℃, the direction of polarization increase slowly. For those three kinds of solution, when\r density increased, the polarization increased observably. When the polarized light passed through the solution with longer path, the direction of polarization has more change. When the wave length of the polarized light changed, the direction of polarization has been changed observably. When the wave length of the polarized light is shorter, the direction of polarization change increased.本實驗主要針對葡萄糖、蔗糖、及果糖等三種旋光性溶液，改變其溫度、濃度、容器管長、以及不同波長的偏振光等因子，觀察這些因素對偏振方向所造成的影響。實驗結果顯示：葡萄糖與蔗糖會使得偏振光的偏振方向以順時針旋轉，屬右旋性之光學異構物；果糖會使得偏振光的偏振方向以逆時針旋轉，屬左旋性之光學異構物。若溶液為葡萄糖，當溫度低於20℃時，偏振光的偏振方向會有明顯的改變，但無規則可尋；當溫度大於20℃時，偏振方向旋轉角位移則以非常緩慢的方式增加。當此三種溶液之濃度增加時，偏振光的偏振方向有明顯遞增的現象。此外，當容器長度越長（即偏振光在介質中的行程越長）時，偏振方向的改變亦越明顯。當偏振光的波長改變時，偏振光的偏振方向有明顯的變化，且當偏振光的波長越短，偏振方向的改變越大，似乎與波長呈反比，但此結果與理論值（即旋光度與波長平方成反比）仍有一些差距。

本研究從大自然中之「蓮花效應」引發學習興趣與研究動機，在蒐集相關資訊與文獻後，發現疏水功能不只是防水，還關係著日常生活品質之許多材料特性，包括防水、撥水、防潮、防銹、防蝕、抗菌防污、自清潔…等。而影響固體表面疏水性之兩大特性，包括物理之表面粗糙度與化學之超低表面能，本研究針對物理之表面粗糙度與疏水性之關係做探討，以相同之化學特性來比較不同號數之工業用砂紙之疏水行為，並就廣泛被引用之兩種模擬表面粗糙度與疏水性關係之模式：Wenzel and Cassie model，比較現有文獻對兩種模式之特性，選擇Cassie model 來進一步實驗驗證，以量測之平均接觸角 Θ 推算Cassie model 之表面粗糙係數Φ 值，並簡化不同砂紙顆粒模型為相同粒徑之球狀，以簡化之方程式來求得水珠與砂紙顆粒之實際接觸面積與球心夾角 θ，以提供高中學校能在經費與設備之限制下，仍能有效應用與印證Cassie model，獲得砂紙顆粒直徑與球心夾角 θ 自然對數值之關係。並就疏水性之生活應用，建立接觸角與 Φ 之關係曲線，驗證實驗之方程式，與延續過去之科展成果，以實驗成果提出可行性應用之建議。The interest and motivation of the present work was introduced from “lotus effect” in nature. After we collected related literature and information, we found that the function of the so-called “superhydrophobicity” behaves not only water repellency, but also a variety of real-life applications, including anti-fog, anti-corrosion, anti-bacteria, anti-fouling, self-cleaning, and so on. Pervious studies have pointed out that two criteria affecting the performance of hydrophobic surfaces are physical (roughness) and chemistry (surface tension) properties. This study focused on influence of physically surface roughness on hydrohyphobicity. Based on an identical surface chemistry, we employed different types of industrial sandpapers to mimic the lotus leaf, and investigated the relationship between roughness and hydrophobicity by using two famous models: Wenzel and Cassie models. Comparing with their basic assumptions to our study, we applied Cassie model to confirm our experimental results, in where one Cassie parameter (?) was proposed to simplify the Cassie equation. This superhydrophobic behavior can be well predicted by the Cassie model. This study continues previous achievement and offers some practical utilization according to our\r experimental results.