What is Faraday: Definition and 213 Discussions

Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction, diamagnetism and electrolysis.
Although Faraday received little formal education, he was one of the most influential scientists in history. It was by his research on the magnetic field around a conductor carrying a direct current that Faraday established the basis for the concept of the electromagnetic field in physics. Faraday also established that magnetism could affect rays of light and that there was an underlying relationship between the two phenomena. He similarly discovered the principles of electromagnetic induction and diamagnetism, and the laws of electrolysis. His inventions of electromagnetic rotary devices formed the foundation of electric motor technology, and it was largely due to his efforts that electricity became practical for use in technology.As a chemist, Faraday discovered benzene, investigated the clathrate hydrate of chlorine, invented an early form of the Bunsen burner and the system of oxidation numbers, and popularised terminology such as "anode", "cathode", "electrode" and "ion". Faraday ultimately became the first and foremost Fullerian Professor of Chemistry at the Royal Institution, a lifetime position.
Faraday was an excellent experimentalist who conveyed his ideas in clear and simple language; his mathematical abilities, however, did not extend as far as trigonometry and were limited to the simplest algebra. James Clerk Maxwell took the work of Faraday and others and summarized it in a set of equations which is accepted as the basis of all modern theories of electromagnetic phenomena. On Faraday's uses of lines of force, Maxwell wrote that they show Faraday "to have been in reality a mathematician of a very high order – one from whom the mathematicians of the future may derive valuable and fertile methods." The SI unit of capacitance is named in his honour: the farad.
Albert Einstein kept a picture of Faraday on his study wall, alongside pictures of Arthur Schopenhauer and James Clerk Maxwell. Physicist Ernest Rutherford stated, "When we consider the magnitude and extent of his discoveries and their influence on the progress of science and of industry, there is no honour too great to pay to the memory of Faraday, one of the greatest scientific discoverers of all time."

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  1. S

    Extended Faraday Disk: How is Energy Conserved?

    In the diagram, I am focusing on the area in the green circle. So this is basically 2 Faraday disk with the magnets opposing and concealed in a copper cylinder. Now if we spin the cylinder a current is generated such as the current following the red arrows. My Confusion: As the current passes...
  2. J

    Faraday Cage and a high voltage discharge arc

    In the following video: I understand how the Faraday Cage works, but what has me confused is the arching. If charge is building up on the sphere and then arching over to the cage, where then is that charge sunk to? You would think it would stop arching when there was sufficient charge on the...
  3. O

    Faraday Cage: Thickness of the conductor

    So i have learned about the ability of Faraday Cage for blocking an external electric field. But is the thickness of the conductor effect the ability? Is there any limit of its thickness so that the cage won't be able to block external electric field anymore? I have read and searched about this...
  4. G

    Transformer equation: Using Faraday's law "the wrong way"?

    Hi. All derivations of the (ideal) transformer equation ##\frac{U_p}{U_s}=\frac{n_p}{n_s}## use Faraday's law of induction $$U=-n\cdot \frac{d\Phi}{dt}$$ for primary and secondary and equate the change of flux ##\frac{d\Phi}{dt}##. Until now, in my textbooks it was always like this: Electrical...
  5. qnach

    Classical Finding the Right Optics Book: Faraday Rotator

    Which book (on optics) can I find talking about Faraday rotator?
  6. Clara Chung

    Why must a Faraday cage be hollow?

    A metal piece has no E field inside too. Why must the microwave use a metal mesh with hollow spaces to block radiation? They can simply use a metal piece just like the interior part of the box.
  7. Dan LaSota

    Faraday Rotation Effect Lab -- sources of components....

    I appreciate the link to the field strength calculator. http://www.calctool.org/CALC/phys/electromagnetism/solenoid I'm also looking for recommendations on sources for magnets. What I'm trying to do is put together a Faraday Rotation Effect Lab. This is my Faraday Rotator, a 12 cm x 2.0 cm...
  8. G

    Faraday cage from Gauss' law alone?

    Hi. Is it possible to derive the properties of a Faraday cage from Gauss' law alone? I found some "derivations" which I find rather unconvincing since they somehow conclude from a vanishing flux that the E field must vanish as well. Some slightly more elaborate derivations use a combination of...
  9. RoboNerd

    Theory in approaching Faraday law/circuit question

    Homework Statement I have a square conducting loop of size L that contains two identical lightbulbs 1 and 2. The magnetic field that goes into the page varies B(t) = a*t + b. Lightbulbs have resistance of R0 Here is a question and the sample response. Disregard the part of the question that...
  10. K

    What Test Tube/Cylinder is suitable for Faraday Effect?

    I am a high school student replicating the Faraday Effect. I plan to insert a clear liquid, such as distilled water, into a container that will be located inside of solenoid. I plan on using a test tube, however, I have doubts on whether or not the curved bottom of a test tube will alter the...
  11. G

    Faraday cage in electrodynamics (with currents)

    Hi. Assume a long hollow wire that both carries a nonzero net charge and a current. Is it still true that all charge sits on the outer surface of the cable and that the empty space inside is field-free (Faraday cage)? I know proofs of those facts in electrostatics using Gauss' theorem, but they...
  12. S

    Faraday Cage: Surprising Facts from SIAM News

    This is an interesting short article from SIAM news that says the Feynman lectures are wrong about the Faraday cage: https://sinews.siam.org/DetailsPage/TabId/900/ArtMID/2243/ArticleID/757/Surprises-of-the-Faraday-Cage.aspx
  13. M

    Faraday's and Lenz law - Experiment with AC coil and Cu ring

    Hi, can someone explain me the next experiment: If I have an AC coil on iron stick, and if I put Cu ring on that stick concentric with AC coil, when I turn coil power supply, the ring will levitate on some height. My question is: Powered AC coil produces an AC magnetic field. If I put a...
  14. K

    Available materials for Faraday rotation experiment

    I am a high school student experimenting with the Verdet constant of materials and how it affects the polarization of light in magneto-rotation. I have trouble acquiring the proper materials for this experiment. Here is what I have so far: -AC/DC Power Supply -Gaussmeter -Optical laser under...
  15. P

    Liénard–Wiechert potentials: Local or Material derivatives?

    If I took a charged particle and accelerated it, that acceleration would have an effect on charges potentials, allowing for the radiation of electromagnetic waves. This acceleration would be local to a point in spacetime and the observed potentials would depend on the frame of reference of the...
  16. P

    Constant Charge/Current Densities with Accelerating Charges

    In classical physics, when electric charges accelerate, they are expected to radiate. Electromagnetic waves, are by their nature the result of changing electric and magnetic fields. But is it possible to have acceleration of charges without having changing electric and magnetic fields? One...
  17. K

    Schools Faraday rotation experiment for a high school student?

    Is it possible to replicate the Faraday rotation experiment for a high school junior? I am in honors physics (IB) and have been taught about waves, electromagnetism, energy transfers, etc. My physics teacher will guide me if I choose to do this. Is the experiment too ambitious?
  18. gsmtiger18

    Line charge creating induced emf and displacement current

    Homework Statement A long, straight wire has a line charge, λ, that varies in time according to: λ = λ0 exp(-βt). A square wire loop of dimension a is located adjacent to the wire at a distance of a from the wire. Calculate expressions for the displacement current at the center of the wire loop...
  19. C

    Electrolysis calcul with faraday

    Hello felow's my boy of 15 years old asked a question about an exercice at college, he asked me how much electricity it would take to generate electrolysis on a sea surface of 100 feet wide and half a mile long. I told him (jocking) you may use some kind of nuclear facilities I thought...
  20. N

    Faraday cage, lower frequencies

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  21. P

    Faraday cage to block cellphone/Wifi?

    Hi, I was wondering if I could make my house a big Faraday cage capable of blocking Wifi and cellphone signals from the outside by covering all of the inside walls with chicken wire? How big of a problem is it that windows would stay uncovered? Or that electrical wiring inside the wall (so...
  22. J

    Does Microwave Mesh Effectively Block Radiation Due to Wavelength or Amplitude?

    Hi pf, Please could someone provide an explanation of why the relationship between the wavelength and size of the gap is the significant factor for determining whether or not it blocks radiation in particular reference to the mesh on the door of a microwave oven. It seems very simple when a...
  23. S

    Faraday Cage in Ionic Solution

    Another question and a another terrible illustration. So my question: do faraday cages interfere with dispersion of ionic solutions? In the illustration, a chemical reaction or some other cause for a lower concentration of ions is happening inside a faraday cage at B. Will the solution disperse...
  24. D

    Faraday Cage not blocking wifi

    In our school we made a submarine. The inner hull is a few cm thick metal, so it should be a good farady cage, but it does not act like one when blocking wifi from inside the hull. Wifi antenna is not touching the hull. The hull acts like a faraday cage when blocking a phone signal from the...
  25. N

    Capacitors in a series circuit W/ one dielectric

    Problem: When a dielectric slab is inserted between the plates of one of the two identical capacitors in Fig. 25-23, do the following properties of that capacitor increase, decrease, or remain the same: (a) capacitance, (b) charge, (c) potential difference (d) How about the same properties of...
  26. Calpalned

    Exploring the Safety of a Faraday Cage: Conductivity and Hollow Design

    Here is what it looks like I have two questions. 1) What if the guy sticks a finger out of the cage? 2) The idea is that it doesn't matter if the cage is solid or hollow (has bars). As long as it's a conductor, the man inside is safe. What if I start removing the bars to make the cage...
  27. A

    Can a cylinder block magnetic fields in one direction like a Faraday cage?

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  28. Dorian Black

    Faraday's Law for a linearly rising magnetic field

    Hi, Imagine a conductive wire bent to the shape of a loop without its ends meeting. A magnet is moved with respect to the loop such that the magnetic field crossing it (perpendicularly) is linearly increasing with time (Φ=kt) where k is a constant. The induced emf is the rate of change of...
  29. J

    Will a Faraday cage affect the efficiency of motors inside?

    "A Faraday cage or Faraday shield is an enclosure formed by conductive material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields by channeling electricity along and around, but not through, the mesh, providing constant voltage on all sides of...
  30. G

    What happens on external surface of the Faraday cage?

    Hello. Let's say we build the Faraday cage which surround strong radiation such that no radiation can escape to outside world for safety. What happens on external surface of the Faraday cage in voltage during shielding? Is it fluctuated?
  31. D

    Question about surface area of faraday cage

    Hi, I am making a faraday cage to be used in reactive ion etching of silicon. I was wondering if the size of the cage, or the surface area has any impact on it's effectiveness or how it works? I know the size of the mesh and the material I use, as well as whether or not it is grounded all...
  32. G

    Grounding of power line filter to Faraday cage chassis?

    Hello. I've uploaded similar question before but I think it is time to make this clear. I've seen the attached one during reading of grounding. In the picture, the body of the power line filter (or ground of the filter) is connected to inner surface of Faraday cage and signal ground is...
  33. V

    Inductor response to applied voltage

    I'm having a bit of trouble wrapping my head around why inductors behave the way they do in certain circuits. Every physical explanation for why ##V = -L\frac{dI}{dt}## that I've seen explains how the voltage across the inductor is developed as the current changes: the changing current means a...
  34. TESL@

    Induced Electric Field inside Faraday Cage

    Imagine there is a hollow toroidal conducting chamber and a long solenoid in the middle. When we power the coil, does the induced electric field "propagate" inside the chamber? My prediction is that the changing flux will cause induction regardless of the cage. Thank you.
  35. anorlunda

    Faraday Cage For Lightning Protection

    A recent thread talked about a radio inside a metal box. That reminds me of a question I never resolved. 9 years ago my sailboat was struck by lightning. 6 people were on board, but nobody was hurt, luckily. My mast is grounded to an underwater plate via a thick copper cable inside a plastic...
  36. J

    Faraday disk/ how is the magnetic flux changing?

    i can not seem to figure out how is the magnetic flux is changing and thus the current is induced , "A "is constant (same disk is spinning ) and "B" is constant and does not change , so how is the current induced ? and more specifically how is the change of magnetic flux is happening ? thanks...
  37. S

    Working with magnetism, solenoid

    Homework Statement A bar magnet is held stationary (with respect to the loop of wire) at the centre of the loop with the North pole sticking out one end and the South pole sticking out the other. What happens to the size of any EMF induced in the loop once the magnet has been replaced by a...
  38. G

    Question for grounding of the electronics to Faraday cage

    Hello. Let's say there is a instrument needed to be EM wave-shielded in High voltage discharge lab. Building Faraday cage becomes necessary and the instrument is moved to inside the cage. The cage is grounded to lab ground and the frame ground of the instrument (it is also signal ground for the...
  39. T

    Does Shaking Harder Create More Charge in a Faraday Flashlight?

    So I have a very basic question, but I have next to no electrical understanding so can't answer it myself. With a Faraday torch you shake a magnet in a coil to create electrical charge. They say the harder you shake the more charge you create, so my question is this... is it the increased...
  40. H

    Detecting the charge distribution within a Faraday cage

    Imagine an uncharged solid spherical conductor. Inside this spherical conductor, there is a cavity of a weird shape carved out of it. And somewhere inside this cavity, there is a charge +q (or rather, a charge distribution of total charge +q). The charge +q induces an opposite charge -q on the...
  41. H

    A puzzle on a Faraday cage "eating up" information

    Imagine an uncharged solid spherical conductor. Inside this spherical conductor, there is a cavity of a weird shape carved out of it. And somewhere inside this cavity, there is a charge +q. The charge +q induces an opposite charge -q on the wall of the cavity of the conductor, which distributes...
  42. J

    Why isn't my Faraday Cage blocking wifi signals?

    So I made this Faraday Cage to block wifi in all directions but 1, to block it from my neighbor. Each side has 6 Layers of aluminum foil on it with no gaps, It looks sloppy because when I tried it and it didn't work I quickly added more trying to make it work. If I put my router inside this...
  43. K

    How Can I Shield My Circuit from EMI Caused by a High-Voltage Pulse Transformer?

    I hit a 1:40 ratio pulse transformer with a 1000V (100mA) sawtooth pulse and it creates a spark gap. Unfortunately it also creates a lot of EMI and my micro-controller and power supply has problems because of it. How do I stop this? How do I know what the wavelength is of the EMI field so I...
  44. C

    Magnetic field rotation or not?

    Suppose for a moment you had a circular copper disc placed concentrically in the air gap between the poles of an upper and a lower circular magnet, the outer faces of the upper lower magnet being connected by a pole piece so as to complete the magnetic circuit. The edge of the copper disc is...
  45. S

    Faraday generator self excited

    Good day, some time ago i asked a similar question but i didnt get a definitive answer. I will try to write as simple as possible, A faraday disc (generator) a constant rpm torque source that spins the generator , now i put some load on the brushes attached to the disc and a capacitor in...
  46. U

    Faraday Tensor and Index Notation

    Homework Statement (a) Find faraday tensor in terms of ##\vec E## and ## \vec B ##. (b) Obtain two of maxwell equations using the field relation. Obtain the other two maxwell equations using 4-potentials. (c) Find top row of stress-energy tensor. Show how the b=0 component relates to j...
  47. J

    Is an induced emf always produced by a change in flux?

    Faradays law tells us that a change in flux induces an emf. Now consider the phenomenon of motional emf. It is observed across the ends of an open conductor (ie one which is not in a circuit). It is always discussed in connection to faradays law. Where is the change in flux in the case of a...
  48. genxium

    Voltage drop across ideal solenoidal inductor

    First by ideal I mean zero resistance. I tried to verify Faraday's law in simple LCR circuit but ran into some conflicting results. Though the description below will be a little verbose, the configuration for this problem is extremely simple: assume that I put a solenoid...
  49. S

    If Faraday invented field concept, how did Newton find g?

    This is Newton's law of universal gravitation. $$F=G\frac{m_1.m_2}{r^2}$$ Gravitational field $$g$$ is derived from this formula $$g=G\frac{m_1}{r^2}$$ This is named gravitational "field" strength. If Newton knew nothing about "field concept" and formulated his formula in the form of "action...
  50. U

    How is the Faraday Tensor related to the 4-potential?

    The Faraday Tensor is given by: Consider the following outer product with the 4-potential: The Faraday Tensor is related to the 4-potential: F^{mn} = \Box^{m} A^n - \Box^n A^m For example, ## F^{01} = -\frac{1}{c} \frac{\partial A^x}{\partial t} - \frac{1}{c}\frac{\partial...
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