MAGNETIC FIELD

MAGNETIC FIELD

Flux Lines. within the area around each magnet there exists a magnetic flux. (A magnetic flux is associate example of the natural phenomenon referred to as a field; another samples of a force field ar the electrical field around each electrical phenomenon and also the force field around each mass.) A magnetic flux will be visualised as consisting of lines of attractive force, or flux, originating at a pole and ending at a South Pole. This direction, from the north to the South Pole, is outlined because the direction of the magnetic flux.

Flux lines haven't any material existence; they're just a convenient thanks to visualize a magnetic flux. However, they will be incontestible physically. a way to try to to this can be to position a sheet of paper over a magnet and sprinkle iron filings on the paper. The iron filings can align themselves on flux lines and convey out the pattern of the magnetic flux. (Jiggling or sound the paper helps to bring out the pattern.) Another technique is to position little compasses at numerous points around a magnet. The compass needle aligns itself on a line of force. If the orientation of the needle is recorded at several locations, the pattern of the sphere can emerge.

Flux lines ne'er cross each other, and that they behave as if subject to 2 competitory forces: every line tries to shrink to the tiniest attainable length, however it's conjointly repelled by the neighboring lines. Thus, a north and a South Pole attract one another as a result of the lines between them try and shrink. within the case of like poles, the lines don't connect one pole to the opposite, and also the poles ar pushed apart as a result of every line is repelled by the neighboring lines and tries to place the maximum amount area as attainable between itself and its neighbors. Here again, it ought to be emphasised that the lines ar just a convenient model.

The strength of a magnetic flux refers to the force that a magnet, a bit of iron, or another check object feels at a specific purpose within the field. Strength is proportional to the concentration of the flux lines. wherever the lines ar targeted (close together), as within the region close to a pole, the sphere is strong; wherever the lines ar way apart, the sphere is weak.

Magnetic-field strength decreases speedily with distance from the magnet. The decrease obeys the inverse sq. law—that is, the strength is proportional to 1/r2, wherever r is that the distance from the magnetic pole. Doubling the space, as an example, reduces the strength to 1 fourth.

Atomic Basis of Magnetism. as a result of matter is created from atoms, and atoms ar charged nuclei enclosed by orbiting electrons, every atom could be a potential magnet. However, the orbital rotation of electrons produces solely a awfully weak magnetic flux. it's the spinning of the electrons as they orbit the atomic nucleus that offers materials magnetic properties. In most substances [*fr1] the orbiting electrons spin in one direction and also the spouse within the reverse direction, thereby canceling any magnetic result. In iron, however, of the fourteen electrons within the third shell (or orbit), the amount of electrons with positive spin doesn't equal the amount of electrons with negative spin. This makes every iron atom act sort of a little magnet; it possesses a property referred to as torsion. in an exceedingly piece of iron, once the magnetic moments ar all aligned within the same direction, the piece of iron as an entire becomes magnetic. This behavior of iron is named magnetism. Iron, nickel, and cobalt, among the alleged transition parts, and a number of other of the rare-earth parts (atomic numbers fifty seven through 71) ar labeled  magnetism as a result of they share iron's magnetic property. as a result of iron displays the strongest magnetism and is lowest in value, it's most typically wont to create magnets. (Several of the rare-earth parts become a lot of powerfully magnetic than iron below temperature.)

Not all iron bars ar magnets. The "atomic magnets," created by a web negatron spin, should be aligned so a majority of them ar orientating in an exceedingly explicit direction. Otherwise the atomic magnets can cancel one another, and also the bar won't be a magnet.

Magnetic properties ar full of temperature. the upper the temperature, the less magnetism there'll be in an exceedingly magnet, till all magnetization disappears at what's referred to as the temperature, or Curie point. The temperature is concerning 770° C (1420° F) for iron, 1120° C (2050° F) for metal, and 358° C (676° F) for nickel. (When a magnet cools, it once more becomes ferromagnetic; but, if it's a static magnet, it's to be remagnetized.)

Electricity and Magnetism. electrical and magnetic phenomena ar intimately connected. One cannot exist while not the opposite, and also the 2 sets of phenomena ar typically referred to as electromagnetism. as an example, each moving electrical phenomenon produces a magnetic flux around itself. as a result of an electrical current could be a flow of electrical charges, a current-carrying wire includes a magnetic flux around it. The magnetic flux lines of this field ar closed loops close the wire. Physicists have long used the "right-hand rule" to recollect the direction of this magnetic flux. Hold the proper hand within the hitchhiker's position: once the thumb points within the direction of the electrical current, the other, curled fingers can purpose within the direction of the magnetic flux. (We ar mistreatment the traditional definition of the direction of an electrical current: the direction is opposite to the direction during which the electrons ar flowing through the wire. an electrical current outlined during this manner typically is just referred to as an electrical current, or typically a standard current; an electrical current outlined as flowing within the same direction because the negatrons is named associate electron current.)

If a current-carrying wire is bent into a loop, the flux lines all bear the loop within the same direction; as a result a magnet is created. The magnet will be created abundant stronger if we tend to bend the wire into several loops—that is, into a spiral or coil—so that there's a bigger concentration of flux lines rummaging the coil. as a result of flux lines choose to bear iron instead of air or empty area, we will concentrate the lines even a lot of by inserting associate iron core into the coil. What we've got now's associate magnet. the nice advantage of associate magnet is that the sphere it creates will be turned on and off by turning this on and off. conjointly the magnetic flux (or poles) will be reversed by reversing the flow of current within the coil.

Magnetic Interactions. A magnet attracts associate unmagnetized piece of iron by turning it into a magnet briefly. as an example, once a magnet is brought close to associate iron or steel staple, the magnetic flux from the static magnet aligns a number of the atomic magnets within the staple, thereby inflicting the staple to become a brief magnet. This briefly magnetic  staple has its South Pole attracted (by manner of its magnetic field) to the pole of the static magnet, and also the staple attaches itself to the magnet. The staple, currently a magnet, will attract alternative paper clips within the same manner. once the staple is aloof from the magnetic flux, its atoms lose their alignment, and also the steel becomes demagnetized.

When electrons ar in motion, they produce a magnetic flux. Therefore, if associate negatron moves through a magnetic flux, the sphere created by the moving negatron can act with the magnetic flux that the negatron is moving through, and also the negatron are going to be deflected from its initial course. Physicists use a "left-hand rule" to indicate the interaction of those forces. The forefinger points within the direction of the magnetic flux (going from north to south); the center finger points within the direction of a positive particle's movement (or the direction from that a negative particle is moving); and also the thumb indicates the direction of the force to that the particle are going to be subjected. the ultimate direction of the particle is decided by the vector of speed|the speed|the rate} imparted by this force and also the initial velocity of the particle coming into the magnetic flux. This deflection of a charged particle (or of a beam of charged particles) is created use of in several devices. In associate microscope, as an example, a beam of electrons traveling on associate exhausted tube is deflected and targeted by magnet "lenses" within the type of coils round the tube. Particle accelerators (atom smashers) use huge magnets to manage the ways of charged particles. tv image tubes, oscilloscopes, and plenty of alternative devices conjointly create use of the deflection of a beam of charged particles by magnetic (and by electric) fields.

A region will be secure from magnetic fields by close it with iron or another magnetic material. The flux lines pass preferentially through the iron and avoid the realm within.

Gaya-gaya Listrik pada Biologi Molekular : Struktur DNA dan Replikasi

Gaya-gaya Listrik pada Biologi Molekular : Struktur DNA dan Replikasi

            Studi mengenai struktur dan fungsi sel hidup pada tingkat molekuler disebut biologi molekuler. Bidang ini penting untuk penerapan fisika. Karena bagian dalam sel terutama terdiri dari air, kita dapat membayangkannya sebagai larutan molekul yang sangat luas yang terus bergerak (seperti pada teori kinetic), yang saling bertumbukan denganenergi kinetic yang beragam besarnya. Molekul-molekul ini berinteraksi satu sama lain dengan berbagai cara—reaksi kimia (membentuk dan memutus ikatan antar atom) dan interaksi atau penggabungan yang lebih singkat yang terjadi karena adanya tarik menarik elektrostatik molekul.

            Banyaknya proses yang terjadi di dalam sel sekarang dianggap sebagai akibat dari gerak molekul acak ditambah efek penyusunan gaya elektrostatik. Kita sekarang menggunakan gagasan-gagasan ini untuk menganalisa beberapa proses seluler dasar yang melibatkan molekul makro (molekul besar). Gambaran ini merupakan model dari apa yang terjadi berdasarkan teori fisika yang pada saat ini diterima dan berbagai macam hasil eksperimen.

            Informasi genetic yang diteruskan dari generasi ke generasi semua benda hidup terdapat dalam kromosom, yang terbuat dari gen-gen. setiap gen berisi informasi yang diperlukan untuk menghasilkan jenis molekul protein tertentu. Informasi genetic yangada pada gen dibentuk menjadi molekul inti pada kromosom, yaitu DNA (deoxyribonucleic acid). Molekul DNA terdiri dari rangkaian panjang molekul-molekul kecil yang dikenal sebagai basa nukleotid. Hanya ada empat jenis basa : Adenine , Cystosine, Guanine dan Thymine.

            DNA pada kromosom umumnya terdiri dari dua rangkaian DNA yang panjang yang saling melilit dengan bentuk “heliks ganda”. Kedua rangkaian diikat oleh gaya elektrostatik yaitu, oleh tarik menarik antar muatan positif dan negative. Bentuk keempat molekul A,T,C dan G adalah sedemikian rupa sehingga T hanya bias berdekatan dengan A, dan G dengan C; dan hanya pada kasus kedekatan bagian yang bermuatan inilah gaya elektrostatik cukup besar untuk mengikat merek bahkan untuk waktu yang singkat sekali pun. Gaya elektrostatik antara A dan T, dan antara C dan G, ada karena molekul-molekul ini mempunyai bagian-bagian yang bermuatan yang disebabkan oleh beberapa electron pada masing-masingnya yang menghabiskan waktu lebih lama untuk mengorbit satu atom dibandingkan dengan lainnya.

            Kromosom membentuk replica dari dirinya sendiri persis sebelum pembagian sel. Dan memang, susunan A berseberangan dengan T dan G bersebrangan dengan C meyakinkan bahwa informasi genetic diteruskan dengan akurat ke generasi selanjutnya. Kedua rangkaian DNA terpisah ((dengan bantuan enzim , yang juga beroprasi melalui gaya elektrostatik), meninggalkan bagian yang bermuatan dari basa terbuka. Tanpa merinci bagaimana replikasi dimulai.

            Gaya elektrostatik tidak hanya mengikat kedua rangkaian, gaya elektrostatik juga bekerja untuk memilih basa dengan urutan yang benar selama replikasi, sehingga informasi genetic diteruskan dengan akurat ke generasi selanjutnya. Kesalahan pada urutan basa memungkinkan untuk terjadi mutasi spontan dan perubahan yang mungkin pada karateristik organism. Nilai kesalahan sebesar nol adalah penting bagi kelangsungan hidup organism, tetapi tidak mungkin bias menjadi nol jika evolusi terjadi.

            Proses replikasi DNA ini sering digambarkan seakan-akan terjadi dengan cara kerja jam seakan-akan setiap molekul mengetahui peranannya dan pergi ke tempatnya yang sudah ditentukan, seperti se ekor lebah pada sarangnya. Tetapi hal ini tidak demikian. Gaya listrik antara muatan listrik molekul agak lemah dan hanya tampak jika molekul-molekul dapat mendekat dan beberapa “ikatan lemah” terbuat. Dan memang, jika bentuknya tidak tepat, hampir ada beberapa kesalahan . intinya adalah ada banyak moleku pada sel semuanya berkeliaran, tetapi hanya sejenis yang memiliki bentuk yang tepat yang akan tertarik sehingga tetap terikat cukup lama pada rangkaian yang tumbuh. Dengan demikian, dari gerakan molekul acak, gaya elektrostatik berperan untuk membentuk keteraturan dan kekacauan.

MAGNETISME

MAGNETISME

            Fenomena magnetic pertama kali diamati sekurang-kurangnya 2500 tahun yang lampau dalam potongan-potongan biji besi yang dimagnetkan yang dijumpai didekat kota kuno magnesia (sekarang Manisa, di turki bagian barat).

            Potongan-potongan ini adalah contoh dari apa yang kita kenal sekarang sebagai magnet permanen; barangkali anda mempunyai beberapa magnet permanen pada pintu lemari es dirumah anda. Magnet permanen terlihat mengerahkan gaya terhadap satu sama lain dan juga pada potongan besi yang tidak dimagnetkan. Telah ditemukan bahwa bila sebuah batang besi disentuhkan dengan sebuah magnet alami, maka batang itu juga menjadi magnet. Bila sebuah batang seperti itu diapungkan pada air atau digantungkan dengan sebuah dawai dari pusatnya, maka batang itu cenderuna menjajarkan dirinya dalam arah utara-selatan. Jarum adalah sebuah kompas biasa adalah sepotong besi yang dimagnetkan seperti itu.

            Sebelum hubunagan interaksi magnetic pada muatan yang bergerak bias dimengerti, interaksi magnet permanen dan jarum kompas dijelaskan dalam kutub-kutub magnet, jika sebuah magnet permanen yang berbentuk batang, atau magnet batang, bebas berotasi, maka satu ujungnya menunjuk arah utara. Ujung ini dinamakan kutub utara atau kutub N; ujung yang lainnya adalah kutub selatan atau kutub S. Kutub-kutub yang berlawanan saling atarik menarik dan kutub-kutub yang sejenis saling tolak menolak.

            Bumi sendiri adalah sebuah magnet. Kutub geografis utaranya dekat ke kutub selatan magnet, dan inilah yang menyebabkan mengapa kutub utara sebuah jarum kompas menunjuk keutara. Sumbu magnet bumi tidak persis parallel dengan sumbu geografisnya, sehingga sebuah pembacaan kompas agak menyimpang dari arah utara geografis. Penyimpangan ini, yang berubah dengan tempat, dinamakan deklinasi magnetic atau variasi magnetic. Juga, medan magnetic itu tidak horizontal dikebanyakan titik pada permukaan bumi; sudutnya yang naik atau turun dinamakan inklinasi magnetic. Di kutub-kutub magnet, medan magnetic itu vertical.

            Konsep kutub magnetic dapat muncul serupa dengan konsep muatan listrik, dan kutub utara serta kutub selatan dapat kelihatan analog dengan muatan positif dan muatan negative. Tetapi , analogi ini dapat menyesatkan. Walaupun terdapat muatan positif dan muatan negative yang terisolasi, namun tidak ada bukti nyata eksperimental terdapatnya sebuah kutub magnet tunggal yang terisolasi; kutub-kutub selalu muncul berpasangan. Jika sebuah magnet batang dipecah menjadi dua bagian, maka setiap ujung yang pecah akan menjadi sebuah kutub. Keberadaan sebuah kutub magnet yang terisolasi, atau monopol magnetic, akan mempunyai implikasi besar untuk fisika teori. Penelitian yang sangat luas untuk monopol magnetic telah dilaksanakan, tetapi sebegitu jauh tanpa hasil.

            Bukti nyata pertama mengaenai hubungan magnetism dengan muatan bergerak ditemukan tahun 1819 oleh ilmuwan Denmark Hans Christian Oersted. Dia menemukan bahwa jarum kompas dibelokkan oleh kawat yang mengangkut arus. Penyeledikan yang serupa juga dilaksanakan oleh Andre Ampere di Perancis. Beberapa tahun kemudian Michael Faraday di Inggris dan Yoseph Henry di Amerika Serikat menemukan bahwa dengan menggerakkan sebuah megnet di dekat sebuah simpal konduktor dapat menyebabkan sebuah arus dalam simpal itu. Kita sekarang mengetahui gaya-gaya magnetic diantara dua benda secara fundamental disebabkan oleh interaksi di antara electron-elektron yang bergerak dalam atom-atom dari benda-benda itu (di atas dan di luar interaksi listrik di antara muatan-muatan ini). Di dalam sebuah benda yang dimagnetkan seperti sebuah magnet permanen, terdapat gerak yang terkoordinasi dari electron-elektron atomic tertentu; dalam suatu benda yang tidak dimagnetkan, gerak ini tidak terkoordinasi dari electron-elektron atomic tertentu.

EFEK FISIOLOGI ARUS

EFEK FISIOLOGI ARUS

Selisih potensial dan arus listrik memainkan peranan yang sangat penting dalam system saraf hewan. Konduksi implus saraf pada dasarnya adalah proses listrik, walaupun mekanisme konduksi itu jauh lebih rumit daripada dalam material sederhana seperti logam. Sebuah serat saraf atau akson, dimana sebuah implus listrik dapat berjalan, mempunyai membrane silindris dengan satu fluida konduksi didalamnya dan fluida konduksi lainnya diluarnya. Dalam kondisi istirahat satu-satunya benda bermuatan yang dapat melewati membrane itu adalah ion kalium bermuatan, yang bocor keluar dari akson itu ke sekitarnya. Ini membiarkan bagian dalam akson itu dengan muatan negative netto dan potensial sebesar kira-kira -70mV terhadap fluida luar.

            Bila sebuah rangsangan listrik diberikan ke akson itu, membrane itu untuk sementara menjadi lebih permeable terhadap ion-ion lain dalam fluida itu, yang menimbulkan perubahan selisih potensial local. Gangguan ini dinamakan potensial aksi, merambat sepanjang membrane itu sebagai sebuah pulsa dengan laju yang ordenya sebesar 30 m/s. keseluruhan pulsa itu melewati sebuah titik tertentu sepanjang akson dalam beberapa milisekon, setelah membrane itu pulih kembali dan selisih potensial itu kembali kenilainya yang semula.

            Sifat listrik dari implus saraf menerangkan mengapa tubuh peka terhadap arus listrik yang diberikan dari luar. Arus melalui tubuh sekecil 0,1 Ampere saja dapat sangat membahayakan, karena arus itu mengganggu proses saraf yang pokok seperti proses saraf dalam jantung. Bahkan arus yang lebih kecil juga dapat sangat berbahaya. Arus sebesar 0,01 Ampere yang melalui lengan atau kaki akan menyebabkan aksi otot kejang yang kuat dan rasa sakit yang cukup besar; dengan arus sebesar 0,02 Ampere, seorang yang memegang konduktor yang membebankan sengatan listrik itu biasanya tidak mampu melepaskan konduktor itu. Arus sebesar ini yang melalui dada dapat menyebabkan fibrilasi kamar (bilik) jantung, yakni kekejangan otot jantung yang memompa sangat sedikit darah. Secara mengherankan, arus yang sangat besar (melebihi 0,1 Ampere) cenderung kurang menyebabkan fibrilasi yang sanag membahayakan karena otot jantung itu “diapit” dalam satu posisi. Jantung itu sebetulnya berhenti berdebyut dan lebih cenderung kembali berdenyut normal ketika arus itu hilang. Defibrillator listrik yang digunakan untuk keadaan darurat pengobatan memberikan pulsa arus yang besar untuk menghentikan jantung itu (dan fibrilasi) untuk member kesempatan pada jantung itu memulihkan irama normalnya.

            Fluida tubuh biasanya adalah konduktor yang cukup baik karena konsentrasi ionnya yang cukup besar. Sebagai perbandingan, hambatan kulit relative tinggi, berkisar dari 500 kΩ untuk kulit yang sangat kering sampai kurang lebih 1000 Ω untuk kulit yang lembab, yang bergantung juga pada luas kontak. Jika R=1000 Ω, sebuah arus sebesar 0,1 A mengharuskan selisih potensial sebesar 100 V. Seandainya bukan karena hambatan tinggi dari kulit, maka naterai senter 1,5 V biasa pun dapat menghasilkan kejutan yang berbahaya.

            Sebagai ikhtisar, arus listrik memiliki 3 macam bahaya berbeda : Interferensi dengan system saraf , cedera yang disebabkan oleh aksi otot kejang, dan luka bakar karena pemanasan. Pesan moral dari cerita yang agak mengerikan ini adalah bahwa dibawah kondisi tertentu tegangan sekecil 10 V pun dapat berbahaya. Semua rangkaian listrik dan peralatan listrik seharusnya selalu ditangani dengan penuh kehati-hatian.

            Pada sisi positifnya, arus bolak-balik dengan frekuensi yang ordenya sebesar 10⁶ Hz tidak berinterferensi secara nyata dengan proses saraf dan dapat digunakn untuk pengobatan melalui pemanasan untuk kondisi penyakit encok, radang membrane lender, dan penyakit lain. Jika suatu elektroda dibuat sangat kecil, pemanasan terkonsentrasi yang dihasilkan dapat digunakan untuk penghancuran jaringan lokan seperti tumor atau untuk memotong jaringan dalam prosedur pembedahan tertentu.

            Kajian mengenai implus saraf tertentu adalah sebuah alat diagnosis yang penting dalam ilmu kedokteran. Contoh yang paling dikenal adalah elektrokardiografi dan electroencephalography. Elektrokardiogram, yang didapat dengan merekam selisih potensial yang berubah-berubah secara teratur, digunakan untuk mengkaji fungsi jantung. Elektroda yang diikatkan ke kulit kepala mengirimkan pengkajian potensial-potensial dalam otak, dan pola yang dihasilkan dapat membantu dalam mendiagnosis penyakit seperti epilepsy atau tumor otak.

SUPERKONDUKTIVITAS

SUPERKONDUKTIVITAS

            Superkonduktivitas ditemukan dalam tahun 1911 oleh Fisikawan Belanda Heike Kamerlingh Oinnes (1853-1926). Dia menemukan bahwa pada suhu yang sangat rendah, dibawah 4,2 Kelvin, resistivitas air raksi tiba-tiba turun ke nol. Selama 75 tahun berikutnya, suhu tertinggi yang dicapai kira-kira 20 Kelvin. Ini berarti bahwa superkonduktivitas hanya terjadi bila material itu didinginkan dengan menggunakan Helium cair yang sangat mahal, dengan suhu titik didih sebesar 4,2 Kelvin atau hydrogen cair eksplosif (mudah meledak), dengan titik didih sebesar 20,3 Kelvin. Tetapi dalam tahun 1987 Karl Muller dan Johannes Bednorz menemukan sebuah Oksida barium, lanthanum dan tembaga dengan sehu tertinggi sebesar hampir 40 Kelvin, dan perlombaan terus berlangsung untuk mengembangkan material superkonduksi bersuhu tinggi.

            Menjelang tahun 1987 sebuah oksida rumit dari titrium, tembaga dan barium telah diperoleh dan memiliki suhu tertinggi diatas 77 Kelvin yang merupakan titik dididh nitrogen cair, yakni sebuah pendingin (refrigerant) yang selain aman juga tidak mahal. Rekor saat ini (1999) untuk suhu tertinggi adalah kira-kira 160 Kelvin, dan material yang merupakan superkonduktor pada suhu kamar mungkin akan menjadi sebuah kenyataan. Implikasi penemuan ini untuk system distribusi daya,rancangan computer dan transportasi akan sangat banyak. Sementara itu electromagnet superkonduksi yang didinginkan oleh helium cair digunakan dalam akselerator partikel dan beberapa rel kereta api levitas magnet eksperimental. Superkonduktor mempunyai sifat-sifat lain yang luar biasa aneh yang meharuskan sebuah pemahaman mengenai magnetism untuk diselidiki.

RESISTIVITAS DAN SUHU

RESISTIVITAS DAN SUHU

            Resistivitas sebuah konduktor logam hamper selalu bertambah dengan suhu yang semakin bertambah, jika suhu bertambah, ion-ion konduktor ini bergetar dengan amplitude yang semakin besar, yang membuat lebih cenderung terjadi tumbukan electron yang bergerak dengan ion, ini merintangi penyimpangan electron melalui konduktor sehingga akan merintangi arus. Pada jangkauan suhu yang kecil (<100˚).

            Resistivitas grafit (non logam) berkurang dengan semakin bertambahnya suhu, karena pada suhu yang lebih tinggi, lebih banyak electron “digoyang lepas” dari atom dan menjadi bebas bergerak; maka koefisien suhu resistivitas grafit adalah negative. Perilaku yang sama ini terjadi untuk bahan semikonduktor. Maka mengukur resistivitas sebuah Kristal semikonduktor yang kecil adalah sebuah pengukuran suhu yang peka; inilah prinsip sejenis thermometer yang dinamakan TERMISTOR.

            Beberapa material termasuk beberapa campuran logam dan oksida, memperlihatkan fenomena yang dinamakan SUPERKONDUKTIVITAS. Jika suhu berkurang, resistivitas itu mulanya akan berkurang secara mulus yang menyerupai konduktivitas sembarang logam. Tetapi pada saat suhu kritis tertentu terjadi peralihan fasa, dan risistivitas itu tiba-tiba turun ke nol. Sekali sebuah arus yang telah ditimbulkan dalam cincin superkonduksi, arus itu berada seterusnya tanpa kehadiran sebarang medan penggerak.

Sumber : Zemansky dan Sears Fisika Universitas

KERUSAKAN DIELEKTRIK

KERUSAKAN DIELEKTRIK

            Jika sebuah material dielektrik dipengaruhi oleh sebuah medan listrik yang cukup kuat , kerusakan dielektrik akan berlangsung dan dielektrik itu menjadi sebuah konduktor. Hal ini terjadi bila medan listrik itu begitu kuat sehingga electron-elektron direnggut lepas dari molekul-molekulnya dan menabrak molekul-molekul lain, yag justru membebaskan lebih banyak electron. Longsoran muatan yang bergerak ini , yang membentuk sepercik bunga api atau bunga api listrik, seringkali muncul tiba-tiba.

            Karena kerusakan dielektrik, kapasitor selalu mempunyai nilai tegangan maksimum. Bila sebuah kapasitor dipengaruhi oleh tegangan yang berlebihan, maka bunga api dapat terbentuk melalui sebuah lapisan dielektrik, yang membakar atau melelehkan material hingga terbentuk lubang didalam lapisan dielektrik itu. Bunga api ini menciptakan sebuah lintasan konduktif (rangkaian pendek) antara konduktor-konduktor itu. Jika sebuah lintasan konduksi tetap ada setelah bunga api itu padam, alat itu secara permanen tidak lagi berguna sebagai kapasitor.

            Besarnya medan listrik maksimum yang dapat ditahan oleh sebuah material tanpa terjadi kerusakan dinamakan KEKUATAN DIELEKTRIK. Kuantitas ini sangat dipengaruhi oleh suhu, ketakmurnian kelumit, ketakteraturan kecil dalam logam, dan factor lain yang sukar untuk dikontrol. Karena alas an ini, maka kita hanya dapat memberikan gambaran aproksimasi untuk kekuatan dielektrik. 

Dielektrik Kapasitor

Mari kita bahas sedikit tentang Kapasitor yang didalamnya terdapat Zat Dielektrik.

Zat dielektrik sendiri adalah material non-konduksi yang dimiliki oleh sebiah Kapasitor yang berada diantara kedua plat konduksinya.  Penambahan sebuah dielektrik padat diantara pelat-pelat sebuah Kapasitor mempunyai tiga fungsi  :

1. Dielektrik menyelesaikan permasalahan mekanis yang mempertahankan dua lembar plat logam tetap terpisah dalam jarak yang sangat kecil tanpa ada sentuhan yang sesungguhnya.
2. Penambahan Dielektrik akan menambah selisih potensial maksimum yang mungkin diantara pelat-pelat kapasitor. Jika material non-konduksi (Dielektrik) dipengaruhi oleh medan listrik yang sangat kuat , akan mengalami Kerusakan Dielektrik , yakni ionisasi parsial yang memungkinkan konduksi melalui dielektrik itu. Banyak material dielektrik yang dapat menolerir medan listrik yang sangat kuat tanpa kerusakan lebih daripada yang dapat ditolerir oleh udara. Penggunaan dDielektrik memungkinkan sebuah kapasitor mempertahankan selisih potensial yang lebih tinggi , sehingga akan menyimpan jumlah muatan dan energi yang lebih besar.
3. Kapasitansi sebuah Kapasitor yang dimensinya tertentu adalah Lebih Besar bila ada sebuah material dielektrik diantara pelat-pelat itu daripada hanya ada ruang hampa. Kita dapat mendemonstrsikan efek ini dengan bantuan Elektrometer yang peka , yakni alat yang mengukur selisih potensial diantara dua konduktor tanpa membiarkan muatan yang cukup besar mengalir dari satu konduktor ke konduktor lainnya. 

Dengan kehadiran Dielektrik , selisih potensial untuk muatan yang diberikan Direduksi oleh sebuah faktor Konstanta Dielektrik  Konstanta Dielektrik adalah sebuah bilangan murni , dimana Konstanta Dielektrik tiap Bahan berbeda-beda tergantung zatnya.

Tidak ada Dielektrik yang benar-benar merupakan isolator sempurna . Maka selalu ada Arus Yang Bocor diantara pelat-pelat bermuatan dari sebuah kapasitor dengan sebuah Dielektrik.

Producing Electrical Current

PRODUCING an electrical CURRENT

An electric charge in motion is termed current. The strength of a current is that the quantity of charge passing a given purpose (as during a wire) per second. The unit for measure current is that the ampere or amp, which is able to be mentioned later during this article. an electrical current is made by natural process or by a generator. altogether cases, we tend to don't seem to be extremely manufacturing this, however rather making the conditions below that electrons will flow.

Chemical Action. a standard supply of electrical current by natural process is that the Leclanche cell, that is employed in devices like the torch. The electric cell, or voltaic battery, conjointly produces a current through natural process.

Dry Cell. A zinc-carbon battery is associate example of a Leclanche cell. It consists of a concave Zn instrumentation, tightly sealed at the highest. The Zn is that the negative conductor. The positive conductor may be a vertical carbon rod set within the middle of the cup and lengthening on the far side the highest. the within of the instrumentation is lined with blotter soaked in ammonium chloride (ammonium chloride). Between the carbon rod and also the blotter may be a pasty mixture of ammonium chloride, fine-grained carbon, and Mn oxide. (The alleged Leclanche cell is merely relatively dry. In weight, it's two-fifths water.) alkaline  batteries square measure similar, however use a unique solution.

How will a Leclanche cell add a flashlight? natural process goes on within the cell whenever you close up the circuit by pressing the switch. this then flows through the circuit, which incorporates the fine wire filament within the little lamp. The flow of the electricity heats the filament, manufacturing visible radiation. once the circuit is broken, this ceases to flow. The natural process is greatly reduced, although not entirely stopped. this is often why batteries in associate unused torch eventually run down. Some slight natural process has been happening, and also the chemicals are exhausted.

Storage Battery. natural process is additionally accustomed manufacture electricity within the voltaic battery. A voltaic battery is recharged and reused again and again. Common storage batteries embrace lead-acid automobile batteries and also the nickel-cadmium batteries employed in several little electronic devices.

A accumulator encompasses a variety of positive electrodes associated an equal variety of negative electrodes, separated from one another by partitions of wood or vulcanite. The solution is sulphuric acid. once the plates square measure charged and prepared to produce current, the positive electrodes square measure composed of lead peroxide, the negative electrodes of spongy lead. In some lead storage batteries, the lead peroxide or spongy lead is contained in holes that are specially punched into the plates.

In a lead electric cell, electrons square measure liberated very much like they're during a Leclanche cell. within the course of your time, each the lead peroxide and also the spongy lead square measure reborn into lead salt. natural process stops, and there's no more flow of current. however it's not necessary to discard the cell. The lead electric cell is fixed up to its former condition by recharging it from some outside supply of electrical current. As current flows into the cell, lead peroxide forms on [*fr1] the electrodes, and spongy lead on the opposite [*fr1]. In associate automobile, the voltaic battery is continually being recharged by a generator hooked up to the motor, as long because the motor itself is running.

Chemical action couldn't offer menage circuits, wherever current is also needed for several hours, day once day. natural process wouldn't manufacture current robust enough for the powerful electrical motors utilized by business, nor might it manufacture the extreme heat of an electrical chamber. to provide robust current or current that has to flow perpetually and over long periods of your time, an electrical generator is required.

Electric Generators. it's virtually not possible to exaggerate the importance of electrical generators these days. while not these machines in power plants, business and business would return much to a standstill. The lights would exit in our homes, schools, and offices. Subways would stop running. we tend to couldn't operate toasters, irons, laundry machines, refrigerators, or microwave ovens. There would be no radio, no tv, no movies, and no computers. Doctors would not be ready to use trendy diagnostic instrumentality on their patients.

The electric generator relies upon the principle called electromagnetism. Hans Christian Oersted (1777–1851), a Danish scientist and chemist, 1st discovered the link between electricity and magnetism. throughout one in all his experiments, he found that the magnet of a compass, that happened to be lying close to wires carrying an electrical current, was deflected at right angles from the north. Oersted ended that an electrical current acts upon a compass very much like a magnet will. It sets up associate magnetic force field.

English scientist and chemist Michael Faraday (1791–1867) took an interest in Oersted's work. physicist argued that if electricity might manufacture a magnetic result, a magnet might, conversely, manufacture associate electrical result. He established that this is often true, and therefore arranged  the muse for the event of the trendy electrical generator.

We know currently that if we tend to pass a conductor, say a wire, through that no current is flowing, between the poles of a powerful magnet, an electrical current is induced  within the conductor. The conductor should kind a part of a electrical circuit. The wire should be affected in such how that it cuts across the lines of magnetic attraction. once the wire is affected upward between the poles of the magnet, the electrons forming this flow in one direction. once it's affected downward, the electrons flow within the different direction. A current that flows 1st approach|a method|a technique|a way} on a conductor so the opposite way is thought as associate electricity. This differs from DC, that flows in one direction only—the kind that we tend to get from dry cells and storage batteries. Some electrical generators manufacture alternating current; others manufacture DC.

STEPPING CURRENT UP OR DOWN

STEPPING CURRENT UP OR DOWN

Electric current is stepped up or down in associate device referred to as a electrical device. This yields stronger current and lower voltage, or weaker current and better voltage. typically it's necessary to own either one combination or the opposite. for instance, it's a lot of convenient for associate electric-power company to send power at a high voltage and low current. However, it's safer and cheaper to use a low-tension and high-current combination in electrical instrumentality within the home.

How will the electrical device work? you recognize that the electrical current passing through a conductor is encircled by its own force field. The strength of this field depends upon the facility of this. It can even be strong by helical the conducting wire; the a lot of coils there area unit, the stronger the force field are. If a second coil of wire is placed close to the primary (but in some way connected), an odd issue happens. once the electrical current within the 1st coil moves in exactly one direction, nothing happens within the second coil despite the fact that it's exposed to the force field of the primary. however once the electrical current within the 1st coil changes direction, because it will in electrical energy, the second coil’s force field additionally changes. The amendment in force field induces an electrical current within the second coil. Current can still flow within the second coil as long because the current within the 1st coil continues to perpetually amendment direction.

A electrical device is used solely with electrical energy. the primary coil, during which electrical phenomenon flows from a supply of electrical energy, is termed the first. The second coil, during which current is elicited, is understood because the secondary. elicited current within the secondary winding perpetually flows within the direction opposite to it within the primary. The force field within the secondary is additionally opposite to it within the primary.

Both the first and also the secondary coils of wire, that are totally insulated, area unit wound around a solid core of iron. The iron core carries the force field back and forth from the first to the secondary, associated during this means it induces an alternating electrical phenomenon within the secondary winding. the quantity of current within the latter depends upon the strength of this within the primary winding, and additionally on the amount of turns within the coils of wire. If there area unit a lot of activates the secondary winding than on the first coil, the voltage is stepped up (that is, increased), and also the current is remittent proportionately. If there area unit a lot of activates the first coil than on the secondary winding, the voltage is stepped down (decreased), and also the current is hyperbolic proportionately.

Without the electrical device, we have a tendency to couldn't use several of our electrical devices. an electrical button, as an example, uses solely a fraction of the complete a hundred and ten volts typically provided to homes. A electrical device is used to step down the voltage from a hundred and ten volts to between five and fifteen volts.

Electricity is generated at terribly high voltages in powerhouses. the electrical current is sent on the wires to distant locations at high voltage (sometimes prodigious two hundred,000 volts) and low current. causation electricity at high current and low voltage would overheat the wires, and far of the electricity would be lost. once this reaches its destination, the voltage is stepped down by a electrical device

ELECTRICITY IN MOTION

ELECTRICITY IN MOTION

In the eighteenth century, scientists began to analyze the probabilities of current electricity—electricity in motion. Scientists Sir Leslie Stephen grey (1666–1736), associate degree English person, and Charles Du Fay (1698–1739), a European, showed that an electrical current might be conducted on metal wires or lengths of hemp string. In 1752, yank politico, scientist, thinker, and publisher Benjamin Franklin (1706–90) performed his far-famed kite experiment. He ready a silk kite with a pointed wire connected to the highest of it. an extended linen string, by that the kite was flown, diode from the wire, and a brief silk ribbon was tied to the top of the string. The linen string served as a conductor, and also the silk ribbon as associate degree stuff. A key was fixed to the string at the place wherever it had been connected to the silk ribbon. once Franklin flew the kite throughout a electrical storm, holding the silk ribbon in his hand, he role player sparks from the key by transportation his knuckle close to it. Thus, he tried that he may draw electricity from the clouds down the wet string to the key.

Franklin knew enough to face underneath a shelter whereas he was activity this experiment. If he had allowed the silk ribbon that he was holding to become wet, it'd became a conductor—and he would most likely are electrocuted. it's still thought-about a quite dangerous experiment, however. A Russian someone was killed trying an equivalent experiment shortly later.

It had become clear by that point that an electrical current might be sent by means that of a conductor from a supply of electricity to another place. Experimenters currently began to analyze sources of provide for dynamic electricity. Galvani (1737–98), a prof of anatomy at the University of Bologna in Italia, took what was most likely the primary step during this direction. physiologist experimented on frogs to seek out out however the nerves build the muscles of the body contract. He discovered that an electrical spark or a flash of lightning would build the legs of a freshly killed frog move violently. In another experiment, physiologist found that once a brass hook connected to the frog's leg came into contact with another reasonably metal, the leg would jump in exactly an equivalent manner. He came to the conclusion that the explanation for this jumping was electricity within the nerve itself—"animal electricity," as he referred to as it.

Alessandro Count Alessandro Volta (1745–1827), prof of physics at the University of Pavia, Italy, was convinced that Galvani's conclusions were wrong which the frog in his experiments had nothing to try and do with the assembly of electricity. "It is evident," Count Alessandro Volta wrote in 1792, "that the explanation for this electricity is within the metals themselves." To prove his purpose, he found out associate degree experiment within which he accumulated silver and metal disks, golf stroke cloths that had been wet in salt water between them. Count Alessandro Volta succeeded in getting electricity from this pile of metal disks, that came to be referred to as the battery. Obviously, what was concerned wasn't "animal electricity," however action between the 2 metals.

Volta's discovery brought the information of electricity to a clearly new part. Previously, it had been potential to charge Leyden jars from static-producing machines, and to discharge them. however it had been much not possible to supply a current that might be created to flow for any considerable length of your time. within the battery, however, current continues to flow at a comparatively steady rate for a substantial amount. this flow relies upon action, therefore it'll still flow as long as this action continues.

ELECTRON MOVEMENT

ELECTRON MOVEMENT

When electrons ar deposited on sure materials, they will create their method freely in and out among the atoms. In sure alternative substances, they can't move freely. they continue to be additional or less at the purpose on the fabric wherever they were deposited. Substances that permit electrons to pass freely through them ar referred to as conductors. They embody such metals as silver and copper. we tend to provide the name of dielectric to a substance that doesn't permit electrons to maneuver through it freely. rubber, mica, glass, and ceramic ware ar all sensible insulators.

The lepton theory explains the workings of electricity. after you charge a rubber comb, you cause a good range of electrons to be cumulous upon it. every lepton repulses its neighbor, however as a result of they're all on associate insulator—the rubber comb—they cannot move apart. If you bring the comb near your ear, you'll hear the noise of electrical sparks as electrons on the comb jump across the air to your ear and rush down from your body into the bottom. Your body could be a fairly sensible conductor. Once within the ground, the electrons move distant from each other. This illustrates a really necessary point—namely, that electrons tend to maneuver from wherever they're in excess to places wherever they will freely opened up. They flow notably to places wherever electrons ar lacking.

You may have detected that after you were hairdressing your hair with a tough rubber comb, the comb created a noise sound. If the area was dark at the time, you'll have seen the small sparks that accompanied  the sound. each the noise and therefore the sparks were caused by electricity. Likewise, if you shuffle your feet on a thick floor covering on a chilly day then bit a metal knob, a spark can jump from your charged finger to the knob, and you'll receive a small electrical shock.

Drivers of petrol trucks need to guard against electricity. Metal-bearing straps droop from the rear of such trucks and drag on the bottom. These straps ar safety devices. They carry to the bottom any sparks of electricity that will be created by the friction of the truck's wheels or by the flow of the petrol into the tank. If the sparks couldn't escape into the bottom on the strap, they may ignite the petrol fumes associated cause an explosion.

An electrical charge of 1 kind will turn out associate opposite charge on a close-by neutral body even once there's no direct contact, if that body could be a conductor. this is often induction. In induction, electrons don't jump from one object to a different. Instead, the shut presence of a charged object causes electrons among the conductor to maneuver. If the thing incorporates a electric charge, electrons within the conductor ar drawn toward it, making a charge on the a part of the conductor nighest to the thing. If the object’s charge is negative, electrons move away, making a electric charge.

Aerodynamics

Aerodynamics is that the study of the flow of air and alternative gases and of the forces functioning on bodies moving through the gases. it's a branch of mechanics, during which a similar principles also are applied to the study of liquids. mechanics is principally utilized to check the flight of aircraft and is therefore mentioned here. it's conjointly accustomed describe the motion of aircraft like dirigibles and to work out the mechanics forces functioning on ground structures. Wind tunnels area unit basic tools of mechanics analysis.

Underlying mechanics and every one alternative branches of theoretical mechanics area unit the laws of motion developed by Isaac Newton within the seventeenth century. These laws state the results of forces functioning on bodies in motion or at rest. Newton conjointly developed the idea of fluid friction, or viscosity—the resistance of air or the other fluid to motion, whether or not its own or that of a body moving through it. A younger modern, Daniel Bernoulli, applied Newton's laws of motion to the study of fluids especially. He developed the principle that the speed of a fluid is said to the pressure at intervals it: the quicker the fluid flow, the lower the pressure. These ideas fashioned the idea for future studies.

AIRPLANE FLIGHT

Such ideas were essential before humans may understand the traditional dream of having the ability to fly through the air. As early because the sixteenth century, applied scientist statue maker had sketched devices resembling the trendy chopper, however while not AN understanding of the mechanics forces concerned on the wing, sensible tries were doomed to failure.

Four main forces act on AN aircraft: thrust, gravity, and therefore the mechanics forces of drag and carry. Thrust and drag work against one another, as do gravity and carry.

An craft moves forward thanks to the thrust equipped by its propellers or jet engines. movement continues as long because the thrust forces area unit larger than the drag forces, that result from the consistence of air. craft area unit thus designed to cut back the maximum amount as potential the drag forces functioning on totally different components of the craft.

In order to beat the Earth's gravity and rise into the air, AN craft should be acted on by a carry force. this is often equipped chiefly by the craft's wings. A wing or alternative surface designed to provide a desired result once acted on by flowing air is named AN device. law forms the idea for the idea of the carry exerted on AN device like a wing. The crosswise of a wing is meant so the angle at that wing meets air causes the air to flow sooner past the wing's side than the lower one. As a result, atmospheric pressure is lower higher than the wing, leading to carry.

MODERN mechanics style

In creating AN mechanics ANalysis of an craft, it's necessary concerning|to contemplate} the element components of the vehicle and to calculate the air flow about every half one by one. The results area unit combined to get the forces functioning on the vehicle as a full. therefore the wing and tail area unit analyzed, and so the passage of air round the body is enclosed as a disturbance of the flow regarding the primary 2. In fashionable mechanics style, the provision of computers has created it potential to check the whole wing, body, and tail configuration.

Designers of high-speed craft should conjointly take under consideration alternative mechanics ideas like the physical phenomenon. this is often the layer of air nearest the skin of the craft wherever the results of the turbulence caused by air resistance area unit exhibited most powerfully. to reduce this turbulence, craft area unit designed to stay the stream of air flowing round the craft as undisturbed as possible—hence the term streamlining.

SUPERSONIC FLIGHT

Such issues become particularly necessary at terribly high speeds. High craft speeds area unit delineate in terms of Mach number, this variety being the quantitative relation of the speed of a given craft to the speed of sound in air of that density. once the 2 speeds area unit equal, the Mach number is one. Speeds but philosopher one area unit referred to as subsonic, those higher than philosopher one area unit supersonic, and people higher than regarding philosopher five area unit referred to as hypersonic.

In the region of philosopher one and higher than, special mechanics issues arise. At lower speeds, the air flowing around a craft will be thought of AN incompressible fluid—that is, a fluid whose density doesn't modification. At high speeds, however, the density of the air will increase sharply, as do its pressure and temperature. To offset this result, supersonic craft fly at a significantly higher altitude than subsonic craft, to submit to agent air. because the craft approaches the speed of sound, shock waves type on its body where the native Mach number exceeds one. because the speed of the craft will increase additional, these shock waves manufacture a shock wave.

The increase in speed from just under to merely higher than the speed of sound is named the sonic speed vary. Fighter pilots of war II cited it as "breaking the sound barrier" once, in flight, their craft entered this sonic region, developing shock waves that storm-tossed the craft. This bump was led to by the unsteadiness of the shock waves at native spots on the wings in sonic flow. At supersonic speeds the shock waves become steady and stay firmly hooked up to the whole craft.

The swept-back wing was designed to delay the formation of shock waves on all craft created to fly at high subsonic speeds. For flying at higher, supersonic speeds, the sweepback is additional multiplied to create a delta wing. Such a wing was seen on the Concorde, that flew at a Mach number of regarding two. solely experimental craft are designed to fly at still higher speeds, within the hypersonic region. for instance, the spacecraft passes through this flight region because it reenters the Earth's atmosphere from orbit, slows down, and makes a standard landing. area vehicles that came back from space before the shuttle weren't flown in however merely created a questionable flight landing.

A characteristic feature of all supersonic flight, and a development even additional characteristic of hypersonic flight, is that the generation of intense heat. this is often caused by friction between the vehicle and therefore the atmosphere. All the K.E. of those fast-moving bodies is regenerate into heat, that successively is dissipated into the atmosphere. to forestall returning artificial satellite from burning up as meteors do once they enter the atmosphere, heat shields are developed. These shields area unit insulated and coated with special material that melts and burns off at a fastidiously controlled rate.

AERODYNAMIC TESTING

Aerodynamic testing is performed extensively, in conjunction with theoretical analysis, so as to achieve a stronger understanding of mechanics issues. Most testing is completed in wind tunnels. regarding four hundred exist within the world, roughly [*fr1] within the u.  s.. Some wind tunnels area unit extremely specialised. they'll generate airflows of short period or in AN intermittent approach, like in massive shock-tubes.

Wind tunnels area unit sometimes classified as subsonic, transonic, supersonic, or hypersonic, in keeping with their Mach-number capability. it's necessary to simulate the air friction of the life-size flight vehicle, however this is {often|this can be} often tough and intensely dearly-won. It needs a awfully massive tunnel and correspondingly massive models or a pressurised tunnel to realize low air-friction. No tunnel has nevertheless been engineered to control at low-friction flow within the supersonic region. laptop modeling is additionally employed in conjunction with wind-tunnel testing, and such models area unit currently obtainable for sonic speeds.