Questions tagged [electromagnetic-induction]

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Induction and electromagnetic fields

I've got a few questions on induction and electromagnetic fields. My current understanding of induction and electromagnetic fields is that, when electricity/current flows through a wire, it creates an ...
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Application of Kirchhoff's laws in circuits with inductors

As we know,the Kirchhoff circuit laws are applicable for conservative electric fields. Now it is applicable for circuits where inductors are present but the field there is not conservative. So how ...
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Faraday's paradox

I have studied that Faraday's law of induction and motional emf are two different lines of thinking but are essentially same. But then, how can Faraday's paradox be explained by Faraday's law of ...
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Can current be induced in a superconductor?

Moving a magnet close to a conductor induces a current. If it consists of a superconducting material with resistance $R=0$, then my textbook says: Then the induced current will continue to flow ...
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1answer
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Induced magnetic field produces electric field and vice versa forever!

So here are the two of Maxwell's laws that I am interested in: So we have the simple circuit (from google): So, before the system goes into steady-state we know that charge slowly accumulates on the ...
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1answer
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Electric field lines forming closed loops

I have been reading about the electric field induced on a metal ring due to an increasing magnetic field directed along the axis of the ring and the electric field lines are found to form concentric ...
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Does changing the electric / magnetic field cause self-reinforcing induction of the other?

I understand that changing electric field produces magnetic field and changing magnetic field produces electric field. Are these produced magnetic and electric field produced due to one defined to be ...
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1answer
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Is there is any way to prove the Faraday's law of induction?

I want to know if there is any way to prove the Faraday's law or is it just an experimental observed phenomena? More specifically, is there any reason why the proportionality constant is 1? How did ...
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1answer
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What is the sum of the electrons' magnetic moments in a wire?

Electrons have magnetic dipole moment. This magnetic moment will be influenced in an electric field in case the electron get moved non-parallel to the current. The magnetic moments will be more or ...
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DC motors, back emf, mechanical power output of a DC motor

In the case of DC motors why is the mechanical power output equal to back emf multiplied by armature current.
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If you are vacuuming your carpet and you wrap the cord around your body do you become a magnet?

If you wrap an active electric cord around your body, do you become an electromagnet?
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Conservation of energy in Lenz's law

When we bring opposite poles of two magnets together, they attract each other (or vice versa). Now, we can say that the kinetic energy gained by the magnets is due to the attractive force. Similarly, ...
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3answers
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Do moving charges get affected by the magnetic field they create while moving to constitute current? If not, how can self-induction be possible?

Let a bunch of charge move with a constant velocity $\mathbf v\;.$ Since, the charges are moving, they would create magnetic field $\bf B$ as it is current that produces magnetic field. Now, would $\...
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How does an inductor store magnetic energy?

I am trying to figure out what the potential energy of an inductor with a current really means. In a capacitor, the energy stored works like this: if you let the plates attract each other, before ...
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2answers
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Is light moving because of self induction? [duplicate]

Light is made by an electric field wave and a magnetic field wave. Induction laws state that a variation in the electric field creates a magnetic field and vice versa. Therefore can it be said that ...
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1answer
482 views

Magnetic Flux conservation

My teacher said that after switch is shifted (after very long time), $\phi_i = \phi_f$ $\implies i_oL = i3L \implies i = \dfrac{i_o}{3} $ where $i_o$ is $\dfrac{\varepsilon}{R}$ So the initial ...
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Simple explanation to the induction from the slowly changing $\vec B$ of a solenoid in the region of $0$ magnetic field

I would like to get some elementary intuition into the problem a solenoid fed with a time-dependent current, and the resulting current that such the solenoid field would induce in a loop completely ...
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4answers
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Why does inductor current lag the applied voltage at its terminal by 90 degrees?

I studied electromagnetism and I am currently working with Inductors. I could not figure out the physical reason based on electromagnetics on why inductor current lags the applied voltage by 90 ...
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1answer
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The fate of a bar magnet released in an infinitely long copper tube

A bar magnet is released under gravity inside a long copper tube along the axis of the tube. The answer is given (edit :) it moves with constant velocity. But I don't understand how. My research : ...
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Why is an $LC$ oscillator lossless, but $C V^2 / 2$ energy is lost to a capacitor connected to an ideal voltage source?

It is mathematically proven that in an $LC$ oscillation that all the energy gets transferred from the inductor to the capacitor and vice versa. There is no energy loss as there is no load in the ...
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3answers
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Violation of energy conservation in retarded interaction of magnet and coil

If I move a magnet towards the coil then the magnet will experience a restive force because of Lenz's law. This way mechanical energy will convert into electrical energy. But what if the magnet and ...
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1answer
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measuring electromagnetic induction

There is a famous law which says that a potential difference is produced across a conductor when it is exposed to a varying MF. But, how do you measure it to prove? It is quite practical. ...
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How does the emf “know” what the magnetic flux is?

I came across an example in my book where it has the changing flux from a solenoid passing through a larger ring at the end. Here's a picture: How does the large loop (or radius $r_1$) even “know” ...
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Kirchoff's rules and inductance

Can Kirchoff's loop rule be applied in a scenario involving an inductor? Kirchoff's loop rule states that the closed loop integral of E dot dl is equal to zero. But, in a situation with an inductor, a ...
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Measuring voltage drop from induced current

I'm having trouble connecting voltage drops and induced current. Imagine you have a triangular loop make up off three resistors. You place this loop in a constantly changing magnetic field. This ...
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3answers
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Explaining Lenz's Law without conservation of energy

I was often told by my professor, using the following example, to demonstrate the relationship of conservation of energy and Lenz's Law. If you push a conductor into a constant magnetic field. By ...
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765 views

How magnetic induction works

What exactly is happening to the electrons inside the wire while it is moving quickly downwards within the magnetic field? Why do electrons move in one direction if the wire is being pushed down? I ...
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Why does a changing magnetic field produce a current?

A changing magnetic field induces a current in a conductor. For example, if we move a bar magnet near a conductor loop, a current gets induced in it. Faraday's law states that The E.M.F. $\...
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1answer
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Calculate electric field induced by a changing magnetic field

I want to plot the electric field (as a vector field plot) which is induced by a changing magnetic field for some simple cases. Suppose for example that the magnetic field changes linearly (or ...
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2answers
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Why is there no induced electric field in the experiment (Faraday's Law)

Below are three circuit diagrams for each of Faraday's experiments that allowed Faraday to come up with Faraday's Law. In Griffiths' Introduction to Electrodynamics Griffiths states (on page 302 of ...
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How did physicists know that only negative charges move?

I have phrased similarly another question about how physicists knew that two charges exist, positive and negative. The purpose of the question is not necessarily to educate me historically. It's just ...
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Rotating bar magnet : current induced in circuit

I don't think this problem makes sense. The answer given is (a). Aren't the field lines parallel to the loop, what does rotation affect ? create atomic currents?
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1answer
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Faraday's law in open circuits

Faraday's law needs a closed loop $\partial\Sigma$ in order to be applied (so as to be able to calculate the magnetic flux across $\Sigma$). However, $\partial\Sigma$ is just, at least according to my ...
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3answers
607 views

How does an Inductor “store” energy?

It seems to me that an electromagnetic field is nothing more than a collection of photons, which as I've heard, extends through space infinitely. Why is it, then, that an inductor such as simple ...
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4answers
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Maxwell-Faraday's Law of Induction Violated?

I am having much distress over Maxwell's 3rd Equation (Faraday's Law of Induction) and a thought experiment I had. Given that Maxwell-Faraday's equation is $$\oint E \cdot ds = -\frac{d\phi}{dt}$$And ...
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Finding the terminal velocity of a magnet dropped in a solenoid

We have to find proportionality of the terminal velocity with the factors of the system: Plot: a small dipole(mass $m$) with dipole moment $\mu$ is dropped in a long solenoid (radius $r$, ...
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2answers
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Em induction, sliding rod with resistance?

Consider the digram below: This consists of a rod sliding with velocity $v$. I want to find the voltage developed between $A$ & $B$. To do this I drew this 'equivalence circuit': From this (...
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1answer
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How a moving electron gets deflected in a magnetic field in on direction and the positron gets deflected in the opposite direction? [duplicate]

In a question Why does nature prefer the right-hand rule over the left-hand rule? was another question My question is, why this direction and not the opposite? This part of the post received no ...
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Why is there no induced current in this loop? [closed]

This problem comes from Barron's SAT Subject Test Physics book. A loop of wire and a bar magnet are moving relative to one another. Which motion in the diagrams shown below will NOT induce a ...
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1answer
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Disc permanent magnet as homopolar generator

It is known that Faraday disk generator produces voltage even when the magnet is rotating along with conducting disk. Does that mean that only rotating, axially magnetized magnet could be used to ...
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2answers
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How does current flow if back emf equals to applied voltage

Suppose we have a circuit with a voltage source, a switch open and an inductor all in series. If we close the switch, the potential difference of the voltage source is instantaneously applied to the ...
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Is the standard explanation for the ring launcher incomplete?

Related: Faraday's law in a ring The ring launcher is a standard introductory physics demonstration that I assume almost everyone has seen (if not, YouTube it). The explanation of why the ring is ...
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How electron get deflected in magnetic field while moving?

I don't understand why electron moves this way... e.g. A light object (crampled paper) going down until gets hit by the wind will go parallel (at least a few seconds) to the wind direction ... why not ...
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How eddy current brakes function

Take the following example: where a rectangular sheet of metal is entering a constant magnetic field at $v \dfrac{m}{s}$. Due to Faraday's law of induction + Lenz's law, we can state that an eddy ...
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Question about inductor

When an inductor is connected with a voltage source we get equal and opposite voltage on inductor against the source voltage. That equal and opposite voltage gradually decreases with time which allows ...
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1answer
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Why can't magnetic flux be no longer defined for non-zero diameter wire?

This is a continuation of my previous question: This is the concerned quote form Purcell's Electricity and Magnetism's Electromagnetic Induction: You may think that one of the rings we considered ...
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Does any object placed in an electric field change the electric field?

Lets say I have a point charge of magnitude $+q$, All around it I would have a symmetric radial electric field. Now if I place a neutral object lets say a sphere (doesn't matter insulating or ...
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When mutual inductance are occurring between two coils, why the two coils have the same mutual inductance?

I learned that $$\epsilon_1 = -M_{12}\frac{di_2}{dt}$$ $$\epsilon_2 = -M_{21}\frac{di_1}{dt}$$ And the book tells us directly that $M_{12} = M_{21}$ without a reason. Is there a mathematical proof ...
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In an AC inductive circuit, the applied voltage is equal to the back emf?

For an inductive coil, the back emf produced is given by $ldi/dt$. In a DC circuit, a power supply, a coil, and a resistance, all in series. when the switch is closed, the back emf becomes equal to ...
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Description of the spiral path of an electron under the influence of a magnetic field

Moving charged particles in an external magnetic field (of course non-parallel to each other) get deflected into a spiral path. For a calculation of this phenomenon it is not sufficient to use the [...