汉语是联合国官方正式使用的 6 种同等有效语言之一。请不要歧视汉语! Chinese is one of the six equally effective official languages of the United Nations. Not to discriminate against Chinese, please! 电磁学(物理学)的基础:磁场的起因 物理学,归根到底是实验科学。 本文的目的: (1)请“实验物理学家”做实验。 (2)请“理论物理学家”提供更多的类似现象。 1971 年 Williams, Faller, Hill 在《 Physics Review Letters 》发表“ New experimental test of Coulomb's law: a laboratory upper limit on the photon rest mass ”, 宣称库仑定律 精确成立。 假如这是 真实的,则表明两个相对静止的点电荷之间没有观测到相互的磁力作用,而只有库仑力的静电相互作用。 在安培 力 ( Ampère's force )公式里,只要两个电流 I 1 、 I 2 的大小一样,则在电流方向相同时的吸引力,以及这两个电流方向相反时的排斥力的大小是相同的。这与毕奥-萨伐尔定律( Biot–Savart law ) 一致。 (1-a ) 安培力(Ampère's force)公式 (1-b ) 安培力(Ampère's force)公式 (2) 毕奥-萨伐尔定律(Biot–Savart law) 问题在于,洛伦 兹 力( Lorentz force )与电荷和磁场之间的相对运动速度有关系。所以,当两个平行导线里的电力方向不同时,代入洛伦兹力公式里的速度V的数值是不一样 的。因此两个载流平行导线之间的磁力,与电流方向有关系。亦即安培定义缺少电流方向的说明。 (3) 洛伦兹力(Lorentz force) 对于点电荷(按 “速度 v ” 做匀速运动),麦克斯韦理论给出的其激发的电场和磁场为: 都是与“速度 v ”有关的。 问题在 于,“ 速度 v ”到底是什么? 法拉第圆盘发电机 ( Homopolar generator: Basic Faraday disc generator ) 在不同的惯性系里, “ 速度 v ” 需要根据不同的观察者的速度 V 进行调整吗? 考虑三根平行导线 a 、b、c ,且该三根导线的直径、材料等均相同。这三根平行导线的横截面呈等边三角形。即如纵向看为平行导线,则横向看其位置为等边三角形。 假设导线 a、b 、c 均通过不同强度的稳恒直流(方向大小都不变的电流),这样对导线 c而 言:导线 a、b 里的电子(电场)速度不相等。 第三根导线 c 受到的洛伦兹力该怎么计算? ① 分别计算与导 线 a、b之间的洛伦兹力 F ac 、 F bc , 再进行矢量合成( F ac + F bc )。 ② 先计算导 线a、b产 生的磁场 B a 、 B b ,用矢量合成的磁场( B a + B b ) 来计算洛伦兹力。 以上两种计算结果相同吗? 假如不同,那个更正确? 核心:洛伦兹力,依赖于电场(电荷)之间的相对速度。 问题: ( 1 )假如库仑定律成立,且磁场与电荷的相对运动速度有关,则在安培力定律( Ampère's force law )中 I 1 、 I 2 的大小,需要考虑它们之间电场或电荷的相对运动 “ 速度 v ” 吗? ( 2 ) 1825年Ampère 的以及 1833 年 Gauss 的实验,实验精度是否足够高?实验现象的解释是否合理? 以下思考题均属于宏观范围问题,请不必考虑量子力学。亦即只在经典电磁学和相对论的范围内思考。 思考题一: 在一个无限大均匀静电场 E 里, ① 一个点电荷 q 按图示方向以 “ 速度 v ” 做匀速运动。请问,该点电荷 q 会受到磁力的作用吗? ② 反过来, 该点电荷 q 静止, 均匀静电场 E (和平板导体) 以 “ 速度 v ” 做匀速运动。请问,该点电荷 q 会受到磁力的作用吗? 思考题二: 在上题里,点电荷换成一个均匀的载流导线,且该导线里流过电流强度为 I 的稳恒直流。 思考题三: 不妨假设上面的“一个无限大均匀静电场”是由平行导体板构成(类似平板电容器)。假设上下两个导体板都做匀速运动,且 v 1 、 v 2 方向相反。请问,这两个导体板之间会出现磁力的作用吗? Homopolar generator: Basic Faraday disc generator https://en.wikipedia.org/wiki/File:Faraday_disc.jpg Michael Faraday ' s experiments in 1831. 相关链接: “高等学校青年骨干教师高级研修班”大会报告,地点:南开大学 二 主楼A203,时间:2008-11-12 上午,《逻辑方法的局限性》. 中国科学院科学智慧火花,2012-04-12,SI基本单位中安培定义的两种可能缺陷 http://idea.cas.cn/viewdoc.action?docid=4681 Williams E R, Faller J E, Hill H A. New experimental test of Coulomb's law: a laboratory upper limit on the photon rest mass . Physics Review Letters, 1971, 26(12): 721-724. http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.26.721 Ampère's force law- From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Amp%C3%A8re%27s_force_law 科学出版社,2015-08-10,科学上过分漂亮的结论很有可能是以无中生有的方式编造 出来的 精选 http://blog.sciencenet.cn/blog-528739-911890.html (3) 19 世纪伟大的化学家 道尔顿 (J. Dalton, 公元1766~1844), 他发明了化学链法则并证明了不同种类原子的存在, 并发表了一系列高深的实验结果. 但是当代的化学家没有一个能再现他所发表的实验结果. (4) 美国物理学家 密立根 (R. Millikan, 1868~1953), 由于他首先测量了电子的电荷而荣获诺贝尔物理学奖. 但是为了让他的实验结果看起来比实际结果更具说服力, 用大量数据伪造了他的工作. 2016-09-06, 一年了,没有人理俺(安培定义的物理实验检验) http://blog.sciencenet.cn/blog-107667-1001173.html 2015-09-06,rainsnow 老师:我的担忧并没有消失!! http://blog.sciencenet.cn/blog-107667-918874.html 感谢您的指教! 感谢您指正以上任何错误!
这个比较新鲜,先是看到网络新闻,后来查到FDA的官方批文。否则,没准还误以为是“伪科学”呢。 FDA的文章里面提到,通过对237个脑癌病人进行的随机临床试验,发现经过电场治疗的病人与化疗的病人有着相似的存活率。另外,两种治疗方法的副作用有所不同。FDA的建议是在其它办法都无效的时候使用这种电场疗法。 详情请看 http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm251669.htm 【这里是研制厂家给出的背景知识 http://www.novocuretrial.com/science.html 】 下面是FDA网站的原文,全文抄袭如下: FDA NEWS RELEASE For Immediate Release: April 15, 2011 Media Inquiries: Erica Jefferson, 301-796-4988, erica.jefferson@fda.hhs.gov Consumer Inquiries: 888-INFO-FDA FDA approves new medical device for form of brain cancer The U.S. Food and Drug Administration recently approved the NovoTTF-100A System , a new device to treat adults with glioblastoma multiforme (GBM) that recurs or progresses after receiving chemotherapy and radiation therapy. Brain tumors are the growth of abnormal cells in the brain tissue. According to the National Cancer Institute, each year about 19,000 people in the United States are diagnosed with primary brain cancers. In 2010, there were 13,140 deaths from brain and other nervous system cancers in the United States. GBM is the most common primary brain cancer. The brain tumor is highly resistant to standard treatments such as surgery, radiation and chemotherapy. When using the NovoTTF-100A System, a health care professional places electrodes on the surface of the patient’s scalp to deliver low-intensity, changing electrical fields called “tumor treatment fields” (TTFs) to the tumor site. The unique shape and electrical characteristics of dividing tumor cells make them susceptible to damage when exposed to TTF, which could stop tumor growth. The device is portable and can be powered with batteries or plugged into an electrical outlet. Patients can use the device at home, allowing them to continue their normal daily activities. “Recurrent glioblastoma multiforme is a devastating form of brain cancer that often eludes standard treatments,” said Jeffrey Shuren, M.D., J.D., director of the FDA’s Center for Devices and Radiological Health. “The agency’s approval of the NovoTTF-100A System shows FDA’s commitment to innovative new devices that provide patients with other treatment options.” The FDA based its approval of the NovoTTF-100A System on results from a single international clinical study in 237 patients with recurrent GBM or with GBM that hadn’t responded to traditional therapy. Patients in the study were randomly assigned to receive either the NovoTTF-100A System or chemotherapy treatment. The study showed comparable overall survival rates between patients treated with the NovoTTF-100A System and those who underwent chemotherapy. Patients treated with the NovoTTF-100A System experienced a slightly higher incidence of neurological side effects including convulsions and headaches compared to patients receiving chemotherapy. However, they did not experience the significant side effects associated with chemotherapy, including nausea, anemia, fatigue and serious infections. A survey of patients in the study suggested an improved quality of life in the NovoTTF-100A recurrent GBM patients compared to patients receiving chemotherapy. Patients should not use the NovoTTF-100A System if they have an implanted medical device or a skull defect, or have a known sensitivity to conductive hydrogels, such as those used with electrocardiograms. The NovoTTF-100A System is not intended to be used in combination with other cancer treatment. The device should only be used after other treatments have failed. The NovoTTF-100A System is made by Novocure of Portsmouth, N.H. For more information: FDA: Medical Devices http://www.fda.gov/MedicalDevices/default.htm FDA: Device Approvals and Clearances http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/DeviceApprovalsandClearances/default.htm NCI: What You Need to Know About – Brain Tumors http://www.cancer.gov/cancertopics/wyntk/brain The FDA, an agency within the U.S. Department of Health and Human Services, protects the public health by assuring the safety, effectiveness, and security of human and veterinary drugs, vaccines and other biological products for human use, and medical devices. The agency also is responsible for the safety and security of our nation’s food supply, cosmetics, dietary supplements, products that give off electronic radiation, and for regulating tobacco products.