# What is Coil: Definition and 900 Discussions

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. ### emf in coil rotating inside magnetic field

My answer is (B) but the answer key is (A). My working: $$\varepsilon=-\frac{d\phi}{dt}$$ $$=-AB\frac{cos\omega t}{dt}$$ $$=AB\omega \sin \omega t$$ Why the answer is zero? I thought the flux will be zero, not the emf. Thanks
2. ### Which way does this coil turn in a magnetic field?

I use FLHR and the plan diagram. This suggests that the left hand side of the coil is going down. I have added annotations to this, which agree with the mark scheme which then goes onto suggest that the coil turns clockwise. To me though this would make it go anti clockwise. So... what am I...
3. ### What factors determine the resistance and inductance in a coil?

Hi what factors determine the resistance and inductance in a coil and they related i.e. if the resistance is high would the inductance be high ? Additionally, would the resistance and inductance value change over time? I only ask this as we tested the resistance and inductance on our coils...
4. ### I Mutual inductance in a transformer

Hello! I have a question regarding the mutual inductance of two coils in a transformer. In the formulas for linked coils ##M=k*\sqrt{(L_1*L_2)}## where ##k=1## for a perfect coupling. I wanted to check my understanding about mutual inductance and see how it can be determined. When I vary the...
5. ### B Current-carrying coil and solenoid

What is the difference between a current-carrying coil and a solenoid?
6. ### Induced EMF in Ansys Maxwell

Hi guys, I'm new to this forum. I'd like to know how I could perform a simulation to find the induced EMF in a coil placed closer to a current-carrying conductor. I'm not sure how I should model the coil. I tried modelling it as a solenoid but the solenoid exceeds my required length when I enter...
7. ### Electrical Help with detecting current/voltage with a coil and a spinning magnet

Playing around with electricity and magnetism. Well, trying to anyways. Wound some wire up and down the length of a 4" screw several times. Thought when I spun the magnet close to the coil I would get a detectable amount of current on my voltmeter. Anyone know why I'm not reading anything? I...
8. ### Back EMF cancelation question with multiple coils wound on the same core

While thinking about back EMF I stumbled upon a curious question. We know that whenever a coil/conductor that passes current is switched OFF and the current is stopped it never stops immediately but instead has a type of "inertia" where the magnetic field created by the current as it passed now...
9. ### B Confusing diagram of a rotating coil in a magnetic field

Hello all, I am currently studying for a physics a-level qualification in the UK, I use the AQA specification and I am having trouble understanding this image representing a scenario I found in my textbook. The first image in the three part diagram shows this rotating coil and to me, it makes...
10. ### B Magnetic field coil ferrous material for loudspeaker

Hi everyone. there are materials called soft magnetic and they are halfway between a permanent magnet and a ferromagnetic material. I would like to try to make a field coil loudspeaker where the maximum amount of flux-density is very important but also the amount of current it takes to create...
11. ### I Coil Around A Tube - Iron Cylinder Inside Tube - How Many Turns Needed?

Hello, I am wanting to wrap a coil of wire around a tube, suspend an iron cylinder in the tube, energize the coil, and have it be able to suspend around 500 pounds on the iron cylinder. I was playing around with some online calculators for coils, and didn't really get anywhere, so I figured I...
12. ### Coil Voltage/Current: Understand Resistance in Relay Circuits

Maybe a not well thought out question: https://cdn.automationdirect.com/static/specs/78relays.pdf 781-1C-24A Relay is listed as having ##177 \Omega## Coil Resistance. I'm assuming that figure will give the Real Power dissipated by the coil (entire relay circuitry) for some current ##I##, or...
13. ### EMF produced across one side of a coil

I want to ask about part c (iii). This is what I did: max e.m.f produced = NBAω = 32 x 0.074 x 4.8 x 10-2 x 2.4 x 10-2 x 2π x 9 = 0.15 V But the answer is 0.077 V so my answer is off by factor of two. Is my mistake related to "emf produced across the side of AC of the coil"? Thanks
14. ### I Quantifying the magnetic force on a magnet moving through a coil?

So I'm familiar with the magnet falling through a copper tube demonstration that shows the induced magnetic fields slowing the magnet down. I know that this experiment is also possible with a conducting coil as long as the coil forms a closed circuit. I'm trying to find a way to calculate the...
15. ### A Does a DC supplied superconductive coil give off radiation?

A DC supplied superconductive electric coil must give off EM radiation according to Maxwell's law because rotation is acceleration. Does it?
16. ### A Coil excitation adjustment on 3D Ansys Maxwell transient analysis

Hi. I am making a 3D Ansys Maxwell project to design DC electromagnet. My model as in attached pictures. I have couple of questions. 1- How important the width value of sheet of coil terminal? Altough I did not change number of conductors and current of coil, changing the width of sheet of the...

18. ### Trace on the screen of a C.R.O. when a deflection coil is rotated

My answer is when the small coil is rotated, there will be change in magnetic flux in it. Initially (before rotated), the trace in c.r.o will be sinusoidal. After it is rotated, the trace will still be a sinusoidal (but I am not sure whether the amplitude will be the same). But the answer key...
19. ### Optimetrics simulation of a coil and moving permanent magnet in Ansys Maxwell

I'm trying to simulate a Magnetostatic problem. In my model there are two coils and a reciprocating permanent magnet. I defined a parameter, Xpm (movement of permanent magnet) in x direction to imply the reciprocating movement of permanent magnet like a piston. Xpm = f(t). I defined "t" as sweep...
20. ### Maxwell 3D & Icepak thermal simulation for a air coil

Hi Guys, I am doing a Maxwell 3D&Icepak thermal simulation for a air coil. I want to get its temperature when loading 1.6A current. So I use Eddy Current type in Maxwell 3D and Temperature and Flow type in Icepak. Then I load 1.6A solid current and adaptive frequency of 800 MHz for the coil...
21. ### Analogue Circuits Question -- AC and DC currents through a coil

Summary:: . Hi ,so am currently doing homework , and was wondering if anyone could tell me if i have done my calculations correctly ,because am not 100% sure that i have answer to those 2 questions correctly .If i have went somewhere wrong if you could tell me where and how i could fix it...
22. ### Do concentric coils steal power from one another?

The amount of power generated by a coil in a changing magnetic field is determined by the area perpendicular to the field, the field strength, and how quickly those values change over time, and is multiplied by the number of loops in the coil. But that made me wonder what would happen if one...
23. ### Why Does the Trigonometric Function in the FEM Calculation Differ?

I need to find the FEM induced in a coil that rotates around the y-axis and is inside a solenoid. The coil starts in the plane yz ##r## is the radius of the coil ##n## is the number of spiral by length of the solenoid. ##N## is the number of turns of the coil ##w## is the angular velocity that...
24. ### I Calculate Diameter of Quad Coil Array for Speed of Light Rotation

I would like to know how to calculate, for any specified frequency in Hz, the required diameter of a 90 degree phased, quadrature coil array such that its generated EM field achieves rotation at the speed of light. Could someone please provide an example of the calculation using a specific...
25. ### Engineering Solve Motor Coil Current at Startup & Full Speed

The question I'm in doubt about is The motor coil has a resistance of 10 Ω and is powered by a voltage of 120 V. When the motor is operating at rated speed, its emf is 70 V. Thus, it is questioned: a) What is the coil current when the motor is started? b) What is the coil current at rated...
26. ### DC versus AC current in a coil

Hello, am kind of new to all the physics stuff , and kind a terrible at maths but am trying my best to be good at it one day .So i was told to answer this question When a direct current of 2A is passed through a coil, the potential difference across the coil is 20V. When an alternating current...
27. ### Coil Compression Spring Reaction to a Pulse

I am trying to understand the reaction of a steel coil compression spring when pulsed. The spring I am interested in has the following physical characteristics: k (spring constant in pounds per inch) = 2.88 d (wire diameter in inches) = .043 n (number of active coils) = 29 D (mean diameter of...
28. ### EMF induced by a magnet falling through a coil

I've been told that if you drop a magnet through a coil the induced emf and flux graphs would look like this: I understand that when the bar magnet is in the middle of the coil the emf induced is zero as flux change in top and bottom is in opposite directions but why is effective flux maximum...
29. ### Calculate energy required to heat water using a steam coil

I'm trying to complete this past exam paper Q. Water volume = 200hl = 20000L 1L=10^-3 m^3 20000L = 200 m^3 Density of water at 15 deg C = 999 kg m^3 Density = Mass/Volume 999 kg m^3 = Mass/(200 m^3) Mass of water = (200)(999) = 199800 kg Heat required to to heat 199800 kg water: Q =m C dT =...
30. ### Electromagnetism - movement of a coil in a magnetic field

So my idea was that to reach the equilibrium position, the final moment of force has to be 0 (so in the end the forces will “eliminate” each other). And I found the equation Fm=B*I*l*sinα, which should characterize the force, which affects wire with the current in a magnetic field, and Fleming’s...
31. ### Find maximum current in a coil using oscilloscopes and Faraday's Law?

The experiment consists of a large field coil (connected to a current source) surrounding a coplanar and coaxial small detector coil in the center of the field coil connected to the oscilloscope. 1. Matching Current v. Time Graphs to Oscilloscope Graphs Example of one pair of graphs (I'll...
32. ### Can i draw a helical coil around a rectangular core in Ansys maxwell?

I am doing core loss calculations in Ansys Maxwell for a project, in which I need to draw a helical coil around a rectangular core to get a more realistic model. But I haven't really found any helpful material. I don't know if its possible, but if it is I would really appreciate your help. Thank...
33. ### Induced current in a square coil by a current-carrying wire

I'll try to explain to you my thinking behind this problem... tell me if it's correct or not. In short, I have assumed the area enclosed between the wire and the left side of the coil to be ##A## in which is present a ##-\hat{z}## field, and noticed that the flux it generates must be canceled by...
34. ### Area-change-rate of a coil generating a given induced current

I managed to solve this problem by writing the total E.M.F. as the sum of the one which would have been induced with only the magnetic field varying(and constant ##A##), and that with only the area varying(and constant ##B##). However, I got to this solution(which doesn't totally convince me)...
35. ### U-Shaped Coil Tokamak: Poloidal Field Control

It is long known that the toroidal field alone is not sufficient to achieve toroidal force balance within a tokamak due to the field being bent and geometry restricting the field to be of even strength both within the inner and outer circumference of the ring. Induced current is thus used for...
36. ### Induced current in a coil from a constant uniform magnetic field?

Assume a solenoid coil(made up of ##N## windings) placed in the horizontal(##\hat{y}##) direction and in a constant uniform magnetic field. Would an induced current run through the(closed) coil if it spins around its central horizontal ##\hat{y}## axis? My guess is "no", since such a current is...
37. ### Changing galvanometer reading in the secondary coil of a transformer?

The present setup is a step-down transformer. Im thinking if n1 is decreased to match or be less than n2, then it will be a step up transformer. so A. (but answers say B)?
38. ### Making a replacement Magnetic coil for my ride-on lawnmower

So voltage is 12v the coil is 80 watts
39. ### Field of a "pancake" coil in QI charger

Attached is a photo the the primary transformer coil of a QI (I believe pronounced CHEE) wireless charger, as used for charging a cell phone. I know the fields of solenoids but what would be the magnetic field structure of this. By-the-way, a similar coil was used on old AM radio sets.
40. ### Why would an electron-emitting heated coil require AC?

Hi. At school, I once worked with a Teltron tube that looked very much like this (I don't remember the brand): The electrons are emitted from a coil that must be heated with a voltage around 5 V. But for some reason, it must be AC, it doesn't work with DC (and it took me a long time of...
41. ### Will EMF be induced in a coil that is accelerating in a uniform magnetic field?

My answer will be no for both (a) and (b) because there is no change in magnetic flux experienced by the circular coil. Am I correct? Thanks
42. ### Direction of force on a voice coil

I want to understand the direction of force on the voice coil, if the conductor is straight line it is easy to find the force direction. In the case of the diagram i shown below, for the curved surfaces i should take tangential to the surface at every point. Am i correct? So for position 1 since...
43. ### Finding the Magnetic force on the coil

Surely a tough one, I am doing it from the basics. This is the diagram i tried to draw showing the Force and current I The Length L is the tangent to the circle. The Force F is pointing upwards at ##90 Deg## to the ##\vec B## and also perpendicular to ##\vec L##. I am considering a small...
44. ### I Equivalence principle: an electric charge and a coil

The near-range magnetic field ##\vec{B}## of a point charge ##q## at distance ##\vec{r}##, moving at a non-relativistic velocity ##\vec{v}##, is given by $$\vec{B}=\frac{q}{4\pi\epsilon_0c^2}\frac{\vec{v}\times\hat{r}}{r^2}.$$ Faraday's law of induction for the induced EMF ##V_c## in a coil...
45. ### A The unwinding coil (teaching experience sharing)

It is just for teaching experience sharing. Consider a uniform disk. A stretchless and massless wire has been wound on the disk. The end of the wire is attached to the ceiling. Initially the system is at rest as it is shown at the picture. Then the disk is released. It falls down and rotates and...
46. ### How do you calculate power from a magnet in a coil?

I don't really know but if I were to guess it would be based on how many turns are in the coil, the diameter of the coil and the flux of the magnet. Unfortunately I couldn't find a formula anywhere.
47. ### Mutual Inductance between a coil and a long straight wire

In the given question they have not provided the dimensions of the coil so I assumed it to be very close to the wire and having negligible dimensions compared to the wire . Then EMF induced in the coil due to the current in the wire comes out as M*a . Which when divided by resistance gives...
48. ### DC generator: Induced EMF of a single coil armature

Hi. I am reading a textbook about simple DC generator. The situation is if we are rotating a single armature coil within a constant field B, the induced emf will be (if we are to only think about the magnitude), emf= B*l*W*omegaB = magnetic field l = length of the coil W = width of the coil...
49. ### How Quickly Can a Conical Spring Expand from Compressed to Free Length?

I require a small conical spring to open from its compressed pancake height of its wire diameter to a free length of 11mm > 0.2 seconds (20 milliseconds) The large end outer diameter = 7.80mm. The small end inner diameter must be greater than or equal to 2.75mm. The conical's spring's will be...
50. ### Compass , current carrying coil

a. No, because only permanent magnets are suitable to be used as a compass. b. Yes, but only if the coil doesn't have an iron core. c. Yes, but only if the coil can turn easily. I choose (c) , Is that correct ?