Questions tagged [electromagnetic-induction]

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Time to magnetize iron

How long does it take for the magnetic domains of a piece of iron to align (and form a magnetic field) from the moment it enters in contact with a magnetic field?
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Incident plane wave on metal rings

in this article an incident electromagnetic plane wave on a periodic sequence of square metal rings is considered. The authors say: When the transverse magnetic field faces the vertical strips, it ...
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Stationary conductor in a time varying magnetic field, emf equation

A question has been asked before, but hasn't got a detailed answer. For a conduction loop in a time varying magnetic field, we get the emf as the rate of change of flux in inside the loop. But, in the ...
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Polarity in a magnetized Möbius strip

When a flat iron or Alnico washer is magnetized one of the faces develops a north polarity and the other, south. The geometric shape here is simple. However, when a standard Möbius strip (or one of ...
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What equation should I use to calculate inductance of a wire coil?

I've been working on a project recently which requires me to build an inductor, however in my research I found many different equations (with a range of variables used and giving very different ...
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What will be the direction of the induced current in the loop due to the other loop?

Say I have a circular loop in which current is flowing which is being increased as time passes by. And beside it in the same plane there is another circular loop which isn't connected to any circuit. ...
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Why is the curl of magnetic field $0$ outside the conductor and non-zero inside? [duplicate]

I dont understand why the magnetic field does not curl outside the cable, according to this example, since I would expect the magnetic field lines to go back on themselves around the cable like shown ...
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Mutual inductance - induced magnetic flux in the primary

Let there be two coils, L1 (with self inductance L1), and L2, with self inductance L2. The first coil is connected to a sinusoidal supply, and the second one is connected to a resistor load, as shown ...
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What is the significance of the electron's wavelength for Momentum and Energy Resolved Tunneling Spectroscopy (MERTS)?

The technique called momentum and energy resolved tunneling spectroscopy (MERTS) is based on quantum tunnelling, whereby an electron can traverse a barrier which has a thickness of less than 3nm, by ...
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Faraday's law. Why does the induced current flow this way?

We have this stationary loop in a time-varying B-field. The current I (in red) is induced by the changing field B(t). This current in turn induces a B field that opposes the changing field due to ...
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Faraday's law and inductors

We can calculate the voltage across an inductor as $$V=-\frac{d \Phi}{dt}$$ I am not sure why can we write this since an inductor isn't a closed-loop, which is a condition for Faraday's law. I am also ...
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Can you induce motion by changing magnetic field on a body which isn't magnetic?

In this video demonstration of Lenz's law, the narrator starts with a substance which doesn't respond to the magnetic field of a bar magnet yet when he moves the bar magnet in relative motion to the ...
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An attempt to solve Feynman's Disc Paradox

The following paradox is mentioned in the Feynman Lectures on Physics Vol II, Chapter 17, Section 17-4. I have seen various solutions to this paradox across the internet and even on this Stack ...
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Energy density of Induced Electric Field

For electrostatic fields, we write the energy density using $$u = \frac12\epsilon_o E^2$$ is this formula also valid for a non-conservative electric field produced by changing magnetic field? Or, can ...
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Electrostatic Induction Metal vs Insulator

If we have a small dielectric sphere and a point charge, they will experience an attractive force due to electrostatic induction. Likewise, if we have a small metallic sphere and a point charge, they ...
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Faraday's Law (General form) and the Change in flux

For the Introductory E&M class, I am taking this year I was working on some problems involving the general Faraday's Law $$\oint{E.dS}=-\frac{d\phi_B}{dt}$$ I was confused regarding, How we ...
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How can a coil self-induce voltage at $t=0$?

Assume you have a resistor and an inductance in series. When a DC supply is connected at t=0, the coil is inducing an opposing voltage, which is the same as the DC supply's voltage. The current ...
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Current induced into a loop by a wire with increasing current [closed]

I've been stumped by this question, which was part of a multiple choice test I took. The questions wants you to find the current induced into a square conducting loop (length 70cm), given that it is ...
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What would be the induced EMF of a hollow sphere moving in linear direction transverse to a constant magnetic field?

This is how I visualized the question- Now, as we know, induced EMF is the change in magnetic flux- $$ EMF = − \frac{N\Delta\Phi}{\Delta t} $$ And as for the magnetic flux- $$ \Phi_B = \iint_A \...
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Why do we only include core electrons in Larmor diamagnetism?

In the Larmor diamagnetism derivation of a susceptibility $\chi = -\mu_0 \frac{\rho e^2}{6m} <r^2>$, we are told to use the density of core electrons as $\mu$ and not all of the electrons in the ...
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What is the magnitude of the Induced Magnetic Field (From Lenz Law) [closed]

I'm having trouble understanding the following: Assume a closed circular loop with a resistance $R$. A changing magnetic field $B$ flows through the closed loop. The induced EMF is: $$EMF = \frac{-d\...
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Why (physically not mathematically) is the induced EMF of a rotating coil the negative derivative of the graph for flux?

The graphs for a rotating coil of the flux and then the induced EMF looks like this. So I understand mathematically that the emf will be at a maximum when the gradient of the flux is at its biggest. ...
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What is the magnetomotive force exactly?

What is the magnetomotive force defined in terms of the variables of and derived from the Maxwell's equations? The emphasis is on the mathematical derivation. The answer by @NicolasSchmid is wrong as ...
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Electromagnetic induction at the centre of a cylinder with rotating current [closed]

A long circular tube of length 10 m and radius 0.3 m carries a current I along its curved surface as shown. A wire-loop of resistance 0.005 ohm and of radius 0.1 m is placed inside the tube with its ...
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Induced Electric field from uniform magnetic field problem

I am trying to find the magnitude and direction of the induced electric field caused by a uniform magnetic field $ \vec B$, which is perpendicular to the plane of the page. The magnitude of the field ...
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What's the direction of the current in this circle if a magnet is approaching (or distancing from) the circle? [duplicate]

I'm not a native speaker so I don't know how to properly describe the problem I'm having right now We got a circuit, it's a circle, and it's placed at the left. We also have a bar magnet which is ...
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Interaction of a permanent magnet's field with an induced magnet

When you place a material capable of being magnetised into another magnetic field, it will become an induced magnet. (For example placing a nail in the vicinity of a bar magnet). Magnetic field lines ...
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Is this inference about Maxwell's 3rd equation correct?

Am I correct in inferring that a changing magnetic field around a loop of wire produces an electric field perpendicular to that changing magnetic field, which itself ...
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On magnetic fields 'inducing' electric fields

Griffith's Introduction to Electrodynamics, 4th Ed. introduces the concept of Faraday's law by providing us with three experiments: one in which a coil is pulled out of a region of a constant magnetic ...
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I have a doubt in applying KVL when an inductor comes to play in a circuit

When we apply KVL in a circuit containing R and L elements connected to a battery, we write the voltage (or EMF?) across the inductor as EMF= L di/dt. But, according to Faradays law and Lenz law, we ...
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How is $B_p$ directly proportional to $I_p$ in a transformer?

The textbook I am studying from states the following The voltage $V_P$ in the primary coil is directly proportional to the current $I_p$ in the coil $$V_p\propto I_p$$ The magnetic flux density $B_p$ ...
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Verification of Faradays law of EMI

What is the verification for Faraday's law of EMI which involves the change in current and voltage produced by the generator with change in speed of the rotor?
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Why is are induced electric field's non-conservative while static electric fields are conservative?

I have learned that the $E$-field induced by changing magnetic flux, such as in 'motional emf', is non-conservative in nature. I am also aware that static $E$-fields are conservative in nature. What ...
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How to find voltage gradient using electrodes?

I have a capacitor, and between them I have an array of electrodes stacked orthogonal to the capacitor plates. The capacitor is running an AC current, and the electrodes are measuring voltage. What I ...
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Change in voltage across an inductor bulb gets brighter

I am trying to understand ac and induction coils. One of the books I am using has the following diagram: The question states that the value of the voltage is adjusted so that the bulb just lights up. ...
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I don't understand Ampere's circuital law

Since, magnetic field is a vector quantity, two (or more) magnetic fields (when in close proximity) should influence their fields, according to the laws of vector. And by that logic, Ampere's ...
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Does a uniform changing magnetic field necessarily induce a uniform electric field?

I don't understand why, using the curie principle, a uniform (but changing in time) magnetic field doesn't induce a uniform electric field. For example, if I take an infinte cylinder plunged into a ...
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What is the magnetic lines of force for rotor with N/S pole?

All illustrations of direction of force in motor has this form. For the following, i'm confused where is the direction of force. It uses winding and there seems to be current and force in every side ...
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Hypothetical set up with wireless induced voltage, confusion with frequency derivative

B field at distance from the center of a ring. And the set up I built. \begin{equation} {B}_z = \frac{\mu _0}{2}\frac{IR^2}{(\sqrt{z^2+R^2})^{3/2}} \end{equation} My voltage through the large ring is ...
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Simple derivative of current confusion

Say you have some $\textbf{B}$ field from an alternating current, $\textbf B(t) = \textbf{B}_0\cos{\omega \,t}$. And using Faraday law, e.m.f. $\varepsilon$ = turns of a coil $\times$ the time ...
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What shape are the eddy currents in this simplified induction motor?

Consider the following simplification of an AC induction motor. A net magnetic field through the origin of a circle is rotating. The object placed at the origin has a the magnetic field sweep through ...
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In mutual induction driven by a sine wave, is the waveform in the secondary coil also a sine wave?

What will be the waveform in the secondary coil of the transformer if the input is a sine wave of some frequency and constant voltage. Will there be any change in the waveform or will it remain same?
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CoilGun analysis method

I want to simulate a CoilGun system in python. Assume The system circuit as a simple RLC circuit It is the method that I used : I used FEMM software to get force & inductance data at different ...
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How does motional EMF emerge from Jefimenko's Equations?

I have been using Jefimenko's Equations for determining the electric and magnetic fields of a conductive coil with a (possibly changing) current. For most situations of interest this can be done to ...
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Will emf be induced across metal ends of rod placed in time varying magnetic field or eddy current will form?

Basically I want to ask how will current flow in metallic rod placed in time varying magnetic field. Will it flow circular or straight. Please this is a different question I am asking about path of ...
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What does someone mean by the direction of magnetic flux?

As far as I know Magnetic Flux is a scalar quantity being the dot product of two vectors. $$\displaystyle{\phi_B = \int{\vec{B}\cdot d\vec{A}}}$$ Now my question might not be so clear to you. So let ...
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Coupled Coils: direction of the magnetic flux

Reading the description of the dot convention, I have found that it makes use of the direction of the magnetic flow: The corresponding terminals are those which, when the current enters through them, ...
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Questions About Highly Coupled Magnetic Resonance

This is one of very few in-depth sources of information I can find online about Highly Coupled Magnetic Resonance: The last sentence of the third-to-last paragraph says that research is underway that ...
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Why only moving magnet relative to coil makes electric current and one that is stopped relative to coil don't make? [closed]

Can you explain using the fact that electric field and magnetic field are perpendicular each other? I wanna visualize the field and electric current image in my head. I searched this and read some ...
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Deriving magnetic field energy per unit volume for a wire

The magnetic energy per unit volume for an inductor can be derived from the formula: $U=\frac{1}{2}L{I}^{2}$ But how to derive formula for energy per unit volume for a (long) wire. Since there is no ...

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