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

    Faraday's law help -- Induced EMF vs. time graph

    Here is a curve of induced emf against time. We know from Faraday's law that E = -N d(phi)dt and due to the negative sign, clearly E and d(phi)/dt must have opposite signs, i.e if E > 0it would not be possible for d(phi)dt > 0, as then -N d(phi)dt = E <0 , when we already defined E >0, clearly a...
  2. G

    A What is Faraday pulsation and how does it impact radiative transfer?

    I’ve bee reading through “Introduction to spectropolarimetry” by del Toro Iniesta and he mentions Faraday pulsation as a mechanism causing mixing of stokes components in the radiative transfer matrix. This is not rotation, that is separate. Any idea what this is? Thanks john
  3. S

    I The vector math of relative motion of wire-loop & bar magnet

    I was watching this video about how the problem of a wire-loop moving relative to a bar magnet: The case of presuming that the wire-loop is fixed seems to be that the magnetic flux (along the surface normal to the direction of the centerline - call it C) through the wire-loop is changing in...
  4. hagopbul

    I Asking about something that I read on electromagnetic force

    Hello All: read a paper related to electromagnetic force and its applications in acceleration of charges particles , some thing came up in it , they drive a force applied on the particle called Faraday force = [1/2B]* [dB/dt]*m*v B magnetic field , m mass of the particle , v the velocity of...
  5. C

    I A and ϕ inside a Faraday cage?

    Are A and ϕ always zero inside a Faraday cage, like E and B are? If not, can its design be modified to accomplish that? If not, is there an analogous mechanism that'd always have A=0 and ϕ=0 inside?
  6. C

    I Faraday cage made of a real conductor

    A faraday cage made of a perfect conductor would theoretically have a zero E field inside. However, are there cases where a faraday cage made of a real conductor like copper wouldn't block out all EM radiation, like very high or low frequencies? How can the design be improved to make a real...
  7. A13579

    B Does a Faraday Cage trap EMF inside and increase exposure?

    Hi All, I’d like you to weigh in on a debate I’ve been having. I’ve been thinking about a Faraday Cage (FC from now on) but from the opposite perspective. Sure it stops EMF getting in. But does that also mean, if there are items emitting EMF in there, that gets trapped within the room. Taking...
  8. FFXT

    I Faraday induction in constant B field, with non-conduction wires

    A standard textbook problem features a constant B field and a conducting loop that increases in area at constant rate. It is easy to work out the induced EMF and the associated electric field magnitude and direction (CW or CCW). The magnitude of the E field is E = B v where v is a velocity...
  9. D

    A Faraday effect breaks photon interaction laws

    I was taught that photons ( non-ionizing at least) never interact. So Its really bugging me that most info on faraday effect invokes B field as the cause of ( for example) rotation effects. Since EM-waves (IE Photons) themselves propagate a (oscillating) Magnetic field through infinite space...
  10. I

    B Protecting Your Computer from Solar Storms - Is a Faraday Cage Enough?

    How did you find PF?: Via Google search From what I understand in scientific publications, if there is a strong solar storm directed towards the Earth, the effects would be such that any electronic equipment would suffer irreparable damage. I ask, if I put my computer inside a Faraday cage...
  11. V

    Swinging a hanging copper ring with a bar magnet

    I thought of few scenarios and they ended up as follows: The ring must have an induced current. Due to the symmetry of the ring, if one part of the ring feels a force, the part of the ring radially opposite this part will feel a force opposite in direction, since the current will be opposite in...
  12. V

    The Power of Intuition: Exploring Overcharging

    I'm pretty sure the answer is overcharged by intuition. Can someone provide a reason?
  13. Ale_Rodo

    "Barlow's wheel" used as an electrical generator

    In this thread, I hope to find some help in understanding one of the first application of Faraday's law of induction: the "Barlow's wheel". Basically the machine converts electrical power to mechanical, so as you can imagine, a battery, some conductor wires, a horseshoe magnet and a metal wheel...
  14. waazwag

    Induced voltage difference in a magnetic field

    Hi everyone, I'm currently working on the problem listed above. I'm pretty new to electrodynamics, and I'm learning on my own through a book. I was wondering if someone can please help me through this problem. Here are my thoughts:I think I need to use Faraday's Law of Induction for part (a)...
  15. Narayanan KR

    At least One Faraday Tube Between Every Two Unlike Charges in the Universe

    By Classic Coulomb's Law there exists negligible yet non zero force of attraction between two unlike charges in-spite of the distance. However for electrostatic attraction to work we need at-least one Faraday Tube(Lines of Forces) between the attracting charges, does that means...
  16. E

    An electron inside a Faraday cage

    I came across a problem that seemed fairly interesting; it asks what would be the trajectory of an electron released from rest inside a Faraday cage (which is itself within a uniform gravitational field ##\vec{g} = -g\hat{y}##). I didn't quite understand their explanation. They say that...
  17. K

    Eddy currents in Faraday's Law Experiment

    My explanation: A circular coil is connected to an AC supply at a frequency of 30-50 kHz (radio frequency). Therefore, an alternate current will be running through this “primary” coil, producing an alternating magnetic field. This magnetic field periodically decreases in strength, alternating...
  18. J

    I The effect of Faraday braking on the Earth’s orbit

    If you let a magnet free-fall down a copper or aluminum tube, the induced magnetic field in the surrounding conductive medium imposes a braking effect on the magnet, reducing its speed (explained by Lenz’s law). The earth, being a large magnet, is essentially free-falling around the sun. The...
  19. stanley

    Impact of frequency on Faraday cages

    I've been reading about faraday cages. The way I see, it works because the condutor will separate the charges so that the eletric charge inside is 0. Then I saw a lecture in which the professor was carrying a radio and the signal stopped as soon as he entered the cage however we were still able...
  20. E

    How do we show that the interior of a Faraday cage is an equipotential?

    It is possible to show via Gauss' law that the the net flux through a surface within the Faraday cage must be zero, however this is not a sufficient condition for the electric field to be zero. For the electric field to be zero in the interior of the cage, all points within the cage must be at...
  21. Ainokea

    Does My Router Need a Faraday Cage to Protect Me From Harmful Radiation?

    Is there a need to put a household router in a faraday cage to cut down on radiated signals that could damage the human body? I would think the manufacturer's would have shielded what needs to be shielded. I see these advertised on Amazon among other places. My router sits about 6 feet from...
  22. I

    Electromagnetism EMF induction calculations

    A square conducting loop of side length a is in a non-uniform magnetic field. The loop occupies the first quadrant of the xy plane, i.e. the space between the origin (x, y) = (0,0) and the point (x,y) = (a, a). The magnetic field is in the +z direction. Develop an expression for the magnitude of...
  23. L

    Faraday and conservation laws

    Hello to all. Second post here so I apologise if I post to the wrong place with wrong altitude etc We have a schematic of a problem like here: https://www.physicsforums.com/threads/conducting-rod-is-free-to-move-over-a-loop-under-influence-of-b-field.750763/ The conducting rod ab shown in the...
  24. B

    Faraday's Law and the distance from another wire

    Hello, I have a conceptual question regarding Faraday's Law: emf = d/dt(Φ), where |Φ|=|B*A|. My question is does Faraday's Law take into account the distance between the solenoid producing the non-coulombic electrical field (Enc) and a wire circling the solenoid, which now have an emf due to the...
  25. rofldude188

    Faraday's Law - Balloon Problem

    a) Calculate the proposed induced emf along the equator of the balloon. (horizontal equator), at the moment indicated above. $$V(t) = V + Ft \implies \frac{4 \pi r^3(t)}{3} = V + Ft \implies r(t) = \sqrt[3]{\frac{3V+3Ft}{4 \pi}}$$ $$\phi = B \pi r^2(t) = B\pi (\frac{3V+3Ft}{4 \pi})^{2/3}$$...
  26. B

    How to build a Faraday cage to keep a WiFi signal inside?

    I'm working on a wifi device testing box and made the first prototype of the Faraday cage. I need holes because of cooling. For this reason, the box has 3mm diameter holes on the top. The box made from steel, and have 2mm wall thickness. The wavelength around 12,5 cm for 2,4 GHz and 6 cm for...
  27. solzonmars

    How does a Faraday Cage block electric fields?

    Why does a Faraday Cage work? (or more generally, why does the inside of a conducting shell have no electric field if there are charges placed outside it?) I understand that this is the result of polarisation, but why does the polarisation happen to exactly cancel out the field? Could there be...
  28. G

    Request about experiments on the linear-motion Faraday paradox

    The Faraday paradox is a very curious example in the topic of relative motion. An experiment demonstrating the curious results is shown in the video below: This has made me curious about the linear version of the Faraday paradox. A conductor placed atop a magnet, both at rest in one scenario...
  29. R

    Reversing the Faraday effect to get an induced current

    Hi all! I was thinking if it is possible to revert the Faraday effect. If I have a magnetic field, it interacts with EM wave (light) by changing its polarisation. Can I got a variable magnetic field interacting with polarised light so that I can get induced current in a coil? I can understand...
  30. S

    What is the optimal thickness for a Faraday cage to attenuate radio signals?

    Greetings, I have a question regarding the attenuation properties of Faraday cages. More specifically, I'm looking for a generalization I can use to better understand how thick they should be for a given frequency. I did a small experiment by taking a small enclosed aluminum box and placed an...
  31. Celso

    Induced EMF — generator coil area calculation

    Homework Statement What is the necessary area for a generator that produces an emf of ##\mathcal{E} = 150V## when it spins at a ratio of 60 revolutions per second, in a magnetic field of ##B = 0.5 T##? Homework Equations ##\oint_{c} E \cdot dl = \mathcal{E} = -\frac{d}{dt}\iint_{s} B \cdot dS...
  32. F

    Why Do Moments Balance in a Faraday Disk but Not the Forces?

    Hi to everybody! Please: can you help with this problem? A conductive disk with a radius a = 20 cm, with negligible moment of inertia, rotates around its horizontal axis. The disc region around the radius is inserted in a magnetic field B = 0.75 T perpendicular to the disk itself. A mass is...
  33. H

    Can a Faraday cage protect you from electrocution in a nano second?

    In the Faraday cage, after injecting the charge, it takes about a nano second for charge to be distributed over the external surface. Why doesn't one become electrocuted in this very little time (nano second)?
  34. F

    Power line EMI filter + feedthrough filter for a Faraday cage

    Dear forumers, I need a 50hz 250VAC power line filter for an EMI shielding faraday cage. The filter should work between 100khz and 20ghz, attenuation should be >=60dB between 1mhz - 5ghz. Regular power line EMI filters like this don't seem to go that high (only up to a few hundreds of mhz...
  35. G

    Faraday disc: different configuration question

    I started thinking about this again because it never really left my mind. Now we know the three different scenarios for the Faraday homopolar disc,1) The disc rotates while magnet and brushes with the circuit they connect stay stationary in the laboratory reference frame = result , current...
  36. U

    Calculation of Change in Magnetic Flux Linkage Across a Wire

    Homework Statement A straight wire of length 0.20m moves at a steady speed of 3.0m/s at right angles to a magnetic filed of flux density 0.10T. Use Faraday's law to determine the e.m.f. induced across the ends of a wire. Homework Equations E= Nd Φ/dt but N=1 so E= dΦ/dt The Attempt at a...
  37. I

    Electrical version of Faraday effect?

    The Faraday effect is a magneto-optical phenomenon caused by the interaction between light and a magnetic field. Is there a corresponding electrical-optical phenomenon, caused by the interaction between light and an electric field?
  38. J

    Faraday's Unipolar Induction Equation

    Hello all, I have a question regarding Maxwell's Equations and Faraday's unipolar induction equation. If we study the case of a cylindrical magnet with a radius of r which is rotating about its axis with angular velocity w. The electrons within the magnet collide with the moving atoms, causing...
  39. G

    Curious question regarding Faraday disc / induction, etc.

    before I ask anything I know this has been probably talked about a lot in the past from various different angles, yet when I am searching for answers I cannot find a satisfactory answer that would look at it from the perspective I wish so here is my try. I've talked with a mentor of mine about...
  40. P

    Simulating a Faraday Cage

    Hi guys, I'm wanting to simulate faraday cage form, analysing mesh perforations defined by wavelengths of different electromagnetic spectra (eg. radio, microwave, UV etc). Are there any good analysis softwares which I could import a pre-made digital model with these perforations and simulate...
  41. SchroedingersLion

    Faraday Rotator: Optics for Amplifying Laser Light

    Hi, another optics question: In the amplifier of a Laser one can have amplified spontaneous emission (ASE) which is an undesired effect. One of my sheets (appended) suggests one can take countermeasures with so called Faraday rotators. But the way I understand it, these optical isolators will...
  42. G

    Need help with a thought experiment about a Faraday generator

    Hi, I arrived at a paradox today which I cannot explain myself. I was watching some physics videos on youtube and among them some were about lenz law and faraday disc workings. Now I know and understand the classical examples of why there is current generated when the magnet moves together with...
  43. reese houseknecht

    Calculating how to make a homemade capacitor

    Ok, so I am am trying to make a homemade capacitor that is 4700pf and 15kv. polyester at 125 micrometers thick can withstand 15kv so were good. here is the equation i used C=ε0 K A / D Where C = capacitance, ε0 is epsilons constant, K = dielectric constant, A = area of aluminum foil, and D is...
  44. C

    A Faraday Tensor Conflicts: MTW vs. Wikipedia

    Hello, I've found that the Faraday Tensor with both indeces down has in the first line, in MTW Gravitation book (pg 74, eq 3.7), minus the electrical field, while in Wikipedia we find that it is plus the electrical field. Which one is right? Does it depend on the signature of the metric?
  45. G

    Is Faraday Cage able to stop all electromagnetic radiations?

    I'm trying to understand if it does exist something (material, construction) that shiled you against alll kind of electromagnetic radiations. Something that shields you from the lowest frequency radio waves up to the highest frequency gamma rays. I've read about faraday cage but it does not...
  46. A

    Requesting Help Regarding the Cause of the Faraday Effect

    Hey everyone, I seek help regarding the Faraday-effect (change of the polarization angle of a linearly polarized wave in an electric field). I have asked my professor about the topic and learned a lot, but I think I am still lacking one or some crucial points. Here is how I understand the cause...
  47. M

    Faraday Cage Effectiveness versus Frequency

    If inside of a metal (for ex. Aluminum) enclosure, could it potentially create more harm than good if frequencies were able to penetrate due to an imperfectly sealed cage or due to a relatively high power level of frequencies that allowed them to penetrate the metal? If the power level was high...
  48. X

    The electrostatic field of the Faraday cage

    I have a function of the cartesian coordinates x, y, z such that: f = a * ln|sin(px + iqy)| + by + c This equation should be describing the electric field nearby the wall of the Faraday cage. I solved the Laplace equation Δf = 0 and got : p = +/- q, so p = q. I should choose the constants...
  49. alfab

    Why does the speed of the magnet matter in a coil?

    I am currently studying Faraday's law and electromagnets and in class we were told that if you had a coil and say a bar magnet was passed through it the faster the magnetic field was applied to the coil the greater the induced voltage or emf would be. I do not understand why the speed would...