Questions tagged [electromagnetic-induction]

This tag is for questions regarding to electromagnetic induction, a process in which a conductor is put in a particular position and magnetic field keeps varying or magnetic field is stationary and a conductor is moving. Electromagnetic Induction was first discovered way back in the 1830’s by Michael Faraday.

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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?
Shawn Anderson's user avatar
35 votes
7 answers
5k views

What does the minus sign in Maxwell's third equation imply?

If we write out Maxwell's equations with magnetic charges, we get $$ \begin{align} \nabla \cdot \mathbf{E} &= 4 \pi \rho_e \tag{1}\\ \nabla \cdot \mathbf{B} &= 4 \pi \rho_m \tag{2}\\ -\nabla \...
rayhem's user avatar
  • 517
33 votes
10 answers
10k views

What happens to an inductor if the stored energy does not find a path to discharge?

Suppose an inductor is connected to a source and then the source is disconnected. The inductor will have energy stored in the form of magnetic field. But there is no way/path to ground to discharge ...
Alex's user avatar
  • 1,431
28 votes
2 answers
4k views

Please help identify this physics apparatus!

This was my grandfather’s and have no idea what it is only that it is some piece of physics equipment! The main black cylinder doesn’t seem like it wants to rotate but not sure if it should?
user37250's user avatar
  • 555
23 votes
4 answers
3k views

Magnetic field changes induced by vibrating electric guitar string

Here is a picture (from a paper by Feinberg and Yang in the Journal of the Acoustical Society of America) of an electric guitar string vibrating (mostly in the $y$ dimension) near a permanent magnet. ...
Wandering Logic's user avatar
14 votes
1 answer
2k views

Induction cooking: why ferromagnetic pan?

In the image above, we have the principle of induction cooking. An alternating current is run through the coil, which causes a change in flux. This change in flux induces eddy currents in the ...
Stallmp's user avatar
  • 633
13 votes
3 answers
3k views

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 ...
George Smyridis's user avatar
13 votes
3 answers
3k views

Why is there an induced EMF in a plastic ring?

If we were to pull a plastic ring across the boundary of a magnetic field, why does an emf form? If this was a metal ring I would fully understand because the electrons are free to move in a metal ...
John Hon's user avatar
  • 2,316
13 votes
4 answers
2k views

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” ...
Astrum's user avatar
  • 1,025
11 votes
5 answers
11k views

Why does a ceiling fan start up slowly? [closed]

I think it probably has something to do with the capacitor inside but I don't get it why doesn't it just Start spinning instantly when we push the button why does it slowly start to spin and gradually ...
iLoveAppSec's user avatar
11 votes
4 answers
29k views

Why Does Change of Magnetic Flux Induce an emf?

Why does change in magnetic flux with time through a coil induce an emf across it? Please explain what happens to the charges in the coil when magnetic flux changes? Also, why does a constant ...
Ankit Agrahari's user avatar
11 votes
3 answers
4k views

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 ...
Jeff Knapowski's user avatar
11 votes
3 answers
1k views

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 ...
ZeroTheHero's user avatar
  • 45.5k
10 votes
7 answers
3k views

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 ...
TanfeexUlhaqq's user avatar
10 votes
1 answer
62k views

Does a positive or negative charge attract a neutral object?

Three objects are brought close to each other, two at a time. When objects A and B are brought together, they attract. When objects B and C are brought together, they repel. From this, we conclude ...
user1527227's user avatar
10 votes
2 answers
2k views

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 ...
hklel's user avatar
  • 280
10 votes
5 answers
7k views

Can you make ice red hot?

This video clip allegedly shows an otherwise unspecified ice cube that turns red hot (and burns) due to induction heating. Can somebody explain how this works?
astabada's user avatar
  • 221
10 votes
3 answers
5k views

How are the Lorentz force, Maxwell's third law and Faraday's law of induction clasically related?

Faraday's law of induction can be used in any situation where the magnetic flux is changing through a closed conducting loop. While giving the correct answer, it seems to me that for the following ...
Coffee-7's user avatar
  • 121
10 votes
1 answer
2k views

What is the physics behind the vibrating feeling you get when you touched an inducted metal surface?

When I was last working on the highway, I stopped to help a motorist parked under high tension power lines. I'm driving a large Ford Transit van, fairly box shaped. My van was parked 90 degrees (...
Angela M.'s user avatar
  • 109
9 votes
3 answers
2k views

How does a wireless charger work if there is no transfer of electrons?

I have read this: the definition of electrical current is the flow of charge. Now, it is also possible to transfer energy (and therefore power) through either free space or a conductor by ...
Árpád Szendrei's user avatar
9 votes
6 answers
40k views

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. $\...
Apoorv Potnis's user avatar
9 votes
3 answers
8k views

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 ...
Steeven's user avatar
  • 51k
9 votes
2 answers
917 views

Does a moving magnetic mirror accelerate particles?

I understand that a magnetic mirror can confine particles within it. Now, suppose I have a magnetic mirror created from two electromagnets : If those two magnets start to accelerate towards the right ...
Waykzen's user avatar
  • 93
9 votes
4 answers
7k views

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 ...
soumyadeep's user avatar
9 votes
2 answers
4k views

Magnetic Levitation : Confusion with Lenz's Law

Considering the above diagram, I am failing to see why the aluminium ring floats upwards rather than oscillates. I understand Faraday's law, but I am struggling with Lenz's law - as there is an ...
DreamsOfHummus's user avatar
8 votes
3 answers
5k views

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 ...
el psy Congroo's user avatar
8 votes
2 answers
8k views

What is the difference between induced and motional emf?

At least from their names, it seems motional emf is induced, so what's the difference?
wrongusername's user avatar
8 votes
4 answers
7k views

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 $\oint\mathbf{E}\cdot d\mathbf{l}$ is equal to zero. But, in a ...
God's Drunkest Driver's user avatar
8 votes
4 answers
7k views

What happens if the load on the electrical generator exceeds its generation power? And why?

What happens if the load on the electrical generator exceeds its power generation? and why? To be more precise, suppose we have a standard induction generator operating at frequency $\nu=50\:\mathrm{...
user44026's user avatar
  • 473
8 votes
3 answers
17k views

Non-conservative electric fields due to changing magnetic flux?

What I read in several places, tells me that, the fact Coulomb's Law follows inverse-square law and gives a force which is radial, implies that a static electric field must be conservative.(In short, ...
stochastic13's user avatar
  • 3,148
8 votes
1 answer
10k views

Why doe we not get a shock on induction cooker?

In induction cooking, eddy currents in cook-pot cause heat to be produced. But why do we not get a shock? Also, why is it that current is converted to heat while it has a good conductor(say, steel) ...
Aadishri's user avatar
  • 225
8 votes
6 answers
2k views

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 ...
Faraz Masroor's user avatar
7 votes
4 answers
941 views

What special properties of magnetic fields allows Faraday's law to work?

Faraday's law states that as the magnetic flux through a loop of wire changes, an EMF is induced around the wire that is proportional to the rate at which the total flux through the loop is changing......
Matt Timmermans's user avatar
7 votes
5 answers
2k views

How to generate electric current without a permanent magnet?

The question is pretty simple: Can we build a device that coverts mechanical work in electric current1 without employing a permanent magnet and without access to any external source of current? The ...
Noumeno's user avatar
  • 4,474
7 votes
2 answers
15k views

Transformer and magnetic field/flux through the iron core?

I am familiar with how a transformer works. This is the diagram that I found on the wikipedia page: The current through the red solenoid varies with time, which creates a time-dependent magnetic ...
SuperCiocia's user avatar
  • 24.7k
7 votes
3 answers
537 views

Why should we expect motional emf to obey the same general relation as Faraday's Law?

There are many posts on this forum asking whether motional emf is actually an instance of Faraday's Law -- because, confusingly, it is often taught as though it is, with no qualification. The best ...
Adam Herbst's user avatar
  • 2,423
7 votes
4 answers
1k views

What is the main mechanism for induction heaters (cookers)?

I thought that induction heaters (as used in cooking) relied on Joule heating losses due to Eddy currents induced by an oscillating magnetic field, produced by an inductor through which AC runs ...
untreated_paramediensis_karnik's user avatar
7 votes
1 answer
1k views

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 ...
Marco Venuti's user avatar
7 votes
2 answers
4k views

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 ...
Mahin's user avatar
  • 363
7 votes
1 answer
306 views

Reversibility of light rays, Faraday effect and Fermat's principle

I am currently having some struggle to understand the connection between the following three concepts in optics: Law of Reversibility (Geometrical Optics): The direction of light rays does not matter ...
cakelover's user avatar
  • 247
7 votes
2 answers
767 views

What is the meaning of Potential Difference in presence of Non-Conservative Induced Electric Field?

Case 1 This is a very commonly discussed case in Electromagnetic Induction. In the case above, we need to find out the potential difference across the rod CD, in the presence of time-varying ...
Devansh Mittal's user avatar
7 votes
1 answer
95 views

Why would a steel tube vibrate under high voltage?

Can anyone explain why a vertical steel tube, standing with one end in contact with the ground under a $230 \space kV$ electric transmission tower, would physically vibrate at high frequency? I'm not ...
Arnie's user avatar
  • 71
7 votes
1 answer
2k views

Motion in a time-dependent uniform magnetic field

Suppose you have an infinite solenoid generating an uniform magnetic field inside. The field is oriented along the solenoid axis : unit vector $\vec{\bf n}$. The field intensity varies linearly with ...
Cham's user avatar
  • 7,470
6 votes
4 answers
4k views

Aren't Gauss's law for magnetism and Faraday's law of induction contradictory?

Gauss's law states that $\int_S \vec B\cdot d\vec S=0$. But law of induction states that $\xi=-\frac {d\phi}{dt}$, where $\phi=\int_S \vec B\cdot d\vec S$. So if Gauss's law was to be correct there ...
Cowgirl's user avatar
  • 87
6 votes
6 answers
11k views

If the wire of the secondary circut is thicker than that of the primary in a transformer, what type of transformer is this and why?

There is this question in my physics book, and two teachers (a private teacher of a friend of mine and the school teacher) say that it's a step down transformer, while two other teachers say that it's ...
Dahen's user avatar
  • 277
6 votes
4 answers
709 views

How do Electric and magnetic fields generate each other (mathematically)?

Regarding electromagnetism, a changing magnetic flux$(\phi_B)$ produces emf by-$$EMF= -\frac{d \phi_B}{dt}\tag1$$ This emf creates a current which again creates a magnetic field given by-(bio-savart ...
SHINU_MADE's user avatar
6 votes
3 answers
1k views

Suspicious EMF equation

Some context: I am trying to get the equation of motion for a dipole magnet falling through copper pipe. To proceed I need to calculate the EMF. We can do this by using Faraday's law, $$\oint_{\...
Edward Henry Brenner's user avatar
6 votes
3 answers
2k views

Confusion in understanding the behavior of inductor in RL circuit with DC source

When we have a DC voltage source with a switch in series with $RL$ and the switch is closed at $t=0$ then it is said that current is zero initially, but the voltage across inductor is same as that of ...
Trilok Girish Kamagond's user avatar

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