Coil Definition and 905 Threads

A coiled coil is a structural motif in proteins in which 2–7 alpha-helices are coiled together like the strands of a rope. (Dimers and trimers are the most common types.) Many coiled coil-type proteins are involved in important biological functions, such as the regulation of gene expression — e.g., transcription factors. Notable examples are the oncoproteins c-Fos and c-jun, as well as the muscle protein tropomyosin.

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  1. P

    Rotational speed of a coil in a magnetic field

    This is for self-study. Homework Statement The armature of a motor has 97 turns each of area 190 cm² and rotates in a uniform magnetic field of 0.33 T. A potential difference of 24 V is applied. If no load is attached and friction is neglected, find the rotational speed at equilibrium...
  2. P

    Charge through a coil in a magnetic field

    Homework Statement At a certain place, the Earth's magnetic field has a magnitude B = 59 μT and is inclined downward at an angle of 70º to the horizontal. A flat horizontal circular coil of wire with a radius of 13 cm has 950 turns and a total resistance of 85 Ω. It is connected to a...
  3. N

    Anti-Helmholtz coil configuration

    Hi Say I have to coils in the anti-Helmholtz configuration as in the attached picture. It is pretty easy to find the field along the z-direction, as this is introduced in introductory EM. However say that I would like to know the field along the x-direction. This I don't know how to find...
  4. O

    Analyzing the Speed of a Permanent Magnet in a Coil

    If a permanent magnet rod enters a coil of wires at a certain speed will the permanent magnet slow down? I'm trying to build a generator of some sort. So i need to know is my logic sound. I'll give you scenario. Scenario: The permanent magnet slides into the coil at a speed of...
  5. P

    Using a DC source to generate a large magnetic field in a coil

    I am a mechanical engineer and I'm working on a project in which I need to generate a large magnetic field in a coil of wire. The current system uses AC power (480V or 230V) and I am exploring the possibility of using a DC battery source. The coil is has an OD of 72mm, an ID of 62mm and a...
  6. I

    Friction with induced coil and magnetic force

    Homework Statement As shown in the attached figure, two rails of conducting wire,M and N, run parallel to each other on a horizontal plane and are separated by distance l. The rails are in a magnetic field of magnetic flux density B that is in the vertically upward direction. An electrically...
  7. A

    What happens when deforming a coil on a magnetic field

    1) Having in mind the Faraday-Lenz law, I'm still not sure if anything happens to it? [1) SOLVED] The area is always the same, the flux idem, flux density as well, so at first glance it would appear nothing happens? This problem was on a exam. 2) Let's say i have a permanent magnet and a...
  8. M

    Coil of supraconductor properties.

    Good day. Can anyone tell me what the difference is the value of magnetic induction B [T] when using the normal driver coil and the coil of superconductor? Thank you.
  9. K

    Forces on electrons inside a coil

    Hi all, First of all, sorry if this is a dumb question but I just wanted to make sure. Imagine the body of an electron microscope and the focusing coils on it. I know that due to the generated magnetic fields, the electrons tend to modify its distance to the central axis in a helix-like...
  10. P

    Charging a capacitor in a tesla coil

    Can somebody explain how it is possible to charge a capacitor using ac voltage? The way I see it is the capacitor wouldn't have time to charge as the voltage is constantly switching. In the case of 60Hz - 120 times a second. I have attached a schematic of a tesla coil which is how I come to...
  11. C

    Length of wire in a coil of known dimensions?

    suppose that i have a wire with a known thickness ... and i want to wind it around a solid cylinder with known dimensions, and in the end make a coil with the same length as the solid cylinder how do i relate between the length of wire required and the diameter of this coil?
  12. I

    Rectangular coil rotating in magnetic field

    Homework Statement A rectangular coil of 80 turns has an area of 0.01m^2. It rotates @ 3000rpm about one of its in plane axes, in a uniform magnetic field having B=1.5T. Calculate the rms voltage generated. Homework Equations 1 Tesla= 1 Weber/m^2. Change in flux of 1 Weber per second...
  13. M

    Calculating Magnetic Field of Solenoid Coil with AC Current

    Hello I want to calculate field of the Solenoid Coil with AC current. For a DC current field is calculated easily from the BiotSavart. What is the process for AC current? Get the L value with RLCMeter in operating frequency? Is there an equation to get the field with...
  14. D

    Does EM Wave induce emf in coil?

    Hi! Does electromagnetic waves induced emf or current in the coil or inductor due to faraday law as the magnetic field is continously changing in em wave?
  15. J

    Orientation of Magnetic Field and Coil

    Homework Statement Not technically a homework problem, has arisen as a point on my A-Level specification and I'm a little unsure as to how they are seeing this situation. "Relate qualitatively the instantaneous e.m.f. induced in a coil rotating at right angles to a magnetic field to the...
  16. J

    Voice Coil Position: Impact of Fringing Field on Dynamic Microphones

    If you have a cylindrical permanent magnet with a voice coil around it, sound moving the voice coil a small distance back and forth along the length of the bar magnet will produce an RMS voltage across the voice coil; but not very much RMS voltage if the voice coil is in the center of the...
  17. Femme_physics

    How can a diode defend the coil during transistor cutoff?

    http://img252.imageshack.us/img252/6080/photo46k.jpg Once the transistor is at cut-off, it means Ib and Ic = 0. I don't see what the diode has to do with anything in terms of "protecting" another component. Can anyone help me see that?
  18. N

    Why a bar magnet or EM coil does not effect EM fields?

    Why is it that a radio wave or a microwave is not affected by a magnetic field from a electromagnet or bar magnet? I know they are self contained and so no outside force should effect them but that I can't get my head around. The idea I have is that since the Electromagnetic field is...
  19. S

    Quick electromagnet coil question

    Hello everyone I have coiled an electromagnet over the weekend using iron and magnet wire, but when I connect it to my power source, the electromagnet becomes very hot. Is there some coating I can use to reduce the heat produced by the electromagnet when in use? Like epoxy or some sort of...
  20. Z

    Problem with calculating magnetic flux for a single coil of wire.

    Homework Statement This is more of a general question about magnetic flux in a uniform magnetic field, but I think this is the correct place to post it. I understand that magnetic flux through an area A is the product of the magnetic flux density B and the projection of area A onto a surface...
  21. baby_1

    Move a object with coil force of magnetic field(formula and Approach)

    Hello i want to move an object with core magnetic filed.could you tell me how can i do that?and what is formula?
  22. N

    Bilifar Coil Inductor Q&A: What Happens When Powered On/Off?

    I have a question about a bilifar coil. First I need to set the image, You have a opposing bilifar coil so as to decrease the inductance of the coil. http://en.wikipedia.org/wiki/Bifilar_coil 1 Winding will be coil A and the other coil B just so we can all know which coil turn we are all...
  23. C

    Maximum current through resistor in a coil of wire with two resistors in parallel

    Homework Statement A coil of wire has 600 turns and is 5.5 cm in diameter is in a magnetic field that decreases from 2.2 T to 0 T in 6.2 ms. The axis of the coil is parallel to the field. The coil is hooked up to two resistors of 120 Ω and 200 Ω connected in parallel. What is the maximum...
  24. M

    Factors that would increase magnetic flux through a coil?

    24. A square coil is perpendicular to a uniform magnetic field. Which one of the following would increase the magnetic flux through the coil? A. Decreasing the area of the coil. B. Increasing the number of loops in the coil. C. Removing the coil from the magnetic field. D. Increasing the...
  25. C

    Induced current due to rotating coil

    I attached a problem from a practice exam. I'm stuck on part b). Part A, I'm assuming the answer is the standard equation for an infinite current sheet. How do I find induced current? I can only think of using Emf = NBA*ωsintωt Where Emf= I/R, but I don't have resistance. Only other equation I...
  26. M

    What self-induced emf appears in that coil?

    Homework Statement The Attempt at a Solution I now know the units are nWb. I'm just getting a little confused by answer. ((6.1mH)(7.3mA))/224turnes=.198795) (mH*mA)/turnes So would that equal= 198.795 nWb?
  27. E

    EMF Induced on Secondary Coil of a Transformer

    Homework Statement http://www.xtremepapers.com/CIE/International%20A%20And%20AS%20Level/9702%20-%20Physics/9702_s02_qp_4.pdf <------ CLICK ON THE LINK The Attempt at a Solution Is the above diagram the correct answer ? Please note that the diagram in the question paper is for COIL...
  28. K

    How can I find the number of turns in a solenoid winding?

    A 30mH solenoid inductor is wound on a form 0.4 m in length and 0.1 m in diameter. A coil is tightly wound around the solenoid at its center. the coil resistance is 5.0 ohms. The mutual inductance of the coil and solenoid is 60μH. At a given instant, the current in the solenoid is 0.3A and is...
  29. E

    Variation in EMF of a magnet moving through a Coil

    NOTE : My Current question and source of debate is in post number 10. Lets say I have a square coil. I accelerate it in a direction such that it is perpendicular to a magnetic field directed into the page. As it enters the field and before it is completely in the field an...
  30. G

    Calculating Induced Current in a Solenoid-Loop Circuit

    Homework Statement A cylindrical solenoid 30 cm long with a radius of 8 mm has 400 tightly-wound turns of wire uniformly distributed along its length (see the figure). Around the middle of the solenoid is a two-turn rectangular loop 3 cm by 2 cm made of resistive wire having a...
  31. L

    Connect a Battery to a Solenoid - Current through a rectangular coil

    Homework Statement Connect a battery to a solenoid A cylindrical solenoid 40 cm long with a radius of 8 mm has 250 tightly-wound turns of wire uniformly distributed along its length (see the figure). Around the middle of the solenoid is a two-turn rectangular loop 3 cm by 2 cm made of...
  32. E

    Average Back EMF Induced in Coil in Loudspeaker

    Hi, I would appreciate any help with the following: The coil in a loudspeaker has an inductance of L = 112 microH. To produce a sound of frequency 40kHz, the current must oscillate between peak values of + and - 4.4 A in half a period. What average back emf is induced in the coil during this...
  33. TestTubeGames

    Tesla Coil as Power Transmitter

    I've been trying to hash this problem out with some friends of mine, but we haven't been able to find a satisfactory answer: Tesla coils are (in an extremely basic sense) like a transformer. There are two coils of wire... the first one having a large current and not-so-large voltage. The...
  34. Y

    Any difference between induced EMF of an air coil vs with magnet core?

    Faraday's Law of Induction: EMF=-\frac{\partial \Phi}{\partial t} If two identical coil with same turns of wire and same dimension ( same cross section area in the middle), one has only air and the other has a magnet core. If the two placed in an uniform varying magnetic field, is there...
  35. H

    Self capacitance of a multi layer coil

    Hi everyone, I am trying to figure out how to correctly calculate the self capacitance of a multi layer coil. I have been trying to find an online calculator or software which can do this but I don't really know where to look. Just hoping someone here can give me some insight. Any help...
  36. B

    Magnetic Field of a Coil Problem

    Homework Statement a positive point charges q= +8.00 μc and q'= +3.00μc are moving relative to an observer at point p (midway between the charges) the distance from on charge to the point is .12 m and one charge moves to the right at 4.5 x 10^6 m/s while the other moves to the left at 9.00 x...
  37. H

    Error tolerance in coil design (number of turns)

    I am designing a coil which will have 2100 turns of 30AWG wire. The bobbin diameter is 1.045" and the length is 1.28" From my calculations I will use about 8,420 inches of wire. I tried an online calc but they did not take into account that the wire I am using has a heavy insulation so it's...
  38. L

    Question: Run-around coil heat recovery systems

    hey guys ,, how are you all ?? guys , I've got the following problem , Air enters a gas-fired furnace at 20deg at a mass flow rate of 0.2kg/s and is burned with an air-fuel ratio by folume of 12. the gases leave the furnace at 350deg. A run-around coil system is installed to recover some of...
  39. M

    Induced Emf in a Rectangular Coil

    Homework Statement A rectangular coil of 90 turns has dimensions of 22 x 65 cm and is located in a uniform 1 T magnetic field. In 1.7 s, the plane of the coil is rotated from a position where it makes an angle of 19° with the magnetic field to a position where it makes an angle of 64°...
  40. H

    Current needed to keep coil levitating

    Homework Statement A horizontally oriented coil of wire of radius r=5.00cm and carrying a current I, is levitated by south pole of a vertically oriented bar magnet suspended above center of coil. If magnetic field (B) on all parts of the coil makes an angle θ=45.0 with the vertical, determine...
  41. L

    Help with a large induction coil secondary

    I am about to build an induction coil in the traditional manner, after "A. T. Hare". The dimensions intimated in the book are confusing and imply there are 96 pies 3/16" each or 18" long - this is the length of the core, and the book indicates around 13" between ends of coils. The book also...
  42. F

    Help with Coil Gun for High School Physics Project

    I am making a coil gun for my high school physics project and I am running into some issues. I am using 400 turns of 36 gauge wire wrapped around a 1.25in diameter PVC pipe to propel a 1 inch diameter steel ball. I started with a 6v battery but that didn't move the ball at all even with...
  43. S

    Voltmeters, transformers coil and short circuit

    A voltmeter must always be connected in parallel right? But when I have a transformer's secondary coil which is connected in series to it, then why is there a voltmeter reading? If i connect a battery in series with a voltmeter, the voltmeter reading will be the voltage of the battery right? So...
  44. S

    Electromagnetic Induction Lab. Magnet through a coil

    I apologize in advance if some of my answers don't quite make sense. I'm generally articulate, but not when it comes to physics I'm barely grasping. I did a lab and part of it was dropping a magnet through a coil, which produced a Voltage vs Time graph using LabPro. For trial 1 we had the N...
  45. E

    Alternator Inductor Coil Output Equation (?)

    Hello!I'm working on an experimental alternating current generator project and need specific equations to calculate voltage and current output from a permanent magnet driven inductor, so I will have an idea what to expect before I commit real money to expensive materials. the only variables...
  46. S

    Average induced emf in coil with turns

    Homework Statement A closely wound rectangular coil of 95.0 turns has dimensions of 29.0 cm by 40.0 cm. The plane of the coil is rotated from a position where it makes an angle of 39.0 degrees with a magnetic field of 1.60 T to a position perpendicular to the field. The rotation takes 0.120 s...
  47. D

    How Does a Tesla Coil Work and How to Build One?

    could you please give me an build structure or the standard model of it's blueprint. Thank you ... Be Ω Thik Ω ! :)
  48. P

    Ignition Coil Won't Spark from Mosfet but DOES spark By Hand? HELP?

    Ignition Coil Won't Spark from Mosfet but DOES spark By Hand? HELP!? I'm trying to get an ignition coil to create sparks running it with a Mosfet powered by a 555 timer. The Mosfet is definitely switching. I checked it with resistor, ampmeter, and o-scope. Everything is behaving predictably...
  49. J

    Inducatnce and Capacitance calculation for rectangular spiral coil

    Hi, I am looking for a formula that calculates self inductance and capacitance of rectangular spiral coil, i came across many formulas for helical coil and circular spiral coil but couldn't find one for rectangular coil, any help is highly appreciated. Thanks
  50. O

    Tesla Coil Safety: Is It Safe?

    On several occasions, I've seen the demonstration where a person holds a fluorescent light bulb up to a tesla coil, and it illuminates. And in general, demonstrators don't seem too worried by the sparks generated. But I was looking at this page, http://www.pupman.com/safety.htm and was...
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