Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now

Questions tagged [electromagnetic-induction]

Filter by
Sorted by
Tagged with
80
votes
4answers
15k views

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?
27
votes
2answers
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?
13
votes
3answers
2k 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 ...
12
votes
4answers
936 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” ...
11
votes
5answers
8k 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 ...
10
votes
2answers
990 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 ...
10
votes
1answer
47k 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 ...
10
votes
5answers
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?
8
votes
4answers
3k 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 ...
8
votes
2answers
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?
8
votes
4answers
19k 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 ...
8
votes
2answers
3k 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 ...
8
votes
3answers
3k 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 ...
7
votes
2answers
2k 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 of E dot dl is equal to zero. But, in a situation with an inductor, a ...
7
votes
1answer
8k 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) ...
7
votes
1answer
83 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 ...
7
votes
1answer
1k 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 ...
6
votes
5answers
5k 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 ...
6
votes
3answers
553 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 ...
6
votes
4answers
395 views

How is it possible for the induced emf to take negative values in Faraday's Law of induction?

Faraday's Law of induction states that the work done per unit charge by the (induced) electric force along a loop of wire, or the emf, is minus the rate of change of magnetic flux through the loop/...
6
votes
4answers
3k 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{...
6
votes
1answer
970 views

Can an induction coil heat two layers of metal?

Imagine we have an induction coil which is strong enough to heat a sheet of metal. We can put a sheet of ferromagnetic metal close to the coil at distance $h_1$, and it gets heated to temperature $t_1$...
6
votes
3answers
297 views

Direction of Hall current

A Hall current arises when electric currents transverse to a magnetic field exist. In this figure (found online), the Faraday current appears to be going upwards due to a magnetic field pointing into ...
6
votes
3answers
3k 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 ...
6
votes
1answer
118 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 ...
6
votes
3answers
7k views

How to find the direction of an eddy current?

Suppose there is a magnetic field going from left to right. Suppose a thin sheet of metal conductor (e.g. a 1m*1m square) is dropped through the magnetic field such that the plane of the conductor is ...
6
votes
0answers
693 views

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 ...
6
votes
0answers
108 views

Weird phenomenon on aluminum laptop casing [duplicate]

A couple of days ago I observed a phenomenon which I'm not sure I understand correctly. My brother-in-law has recently bought an ASUS gaming laptop in an aluminum casing. When the power supply is ...
6
votes
2answers
420 views

What is the area in Faraday's law if we have only a piece of metal moving in a magnetic field?

If a piece of metal of length $l$ is moving with a speed $v$ in a region where there is a uniform magnetic field $B$ perpendicular to it, there will be a potential difference across its terminals ...
5
votes
3answers
4k views

What is the physics behind shake flashlights?

What is the physics behind shake flashlights? From what I have read and from what I have seen when I tore one apart is that it is simply a magnet, coiled wire, a capacitor, and a light bulb. ...
5
votes
3answers
28k views

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, ...
5
votes
2answers
11k 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 ...
5
votes
4answers
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 ...
5
votes
2answers
589 views

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?
5
votes
1answer
10k views

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 ...
5
votes
2answers
7k views

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 ...
5
votes
4answers
766 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 ...
5
votes
3answers
14k 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, ...
5
votes
1answer
2k views

Why an inductor parallel with a light bulb makes it flash as a key closes the circuit?

The title is a simplified form of my question. To be precise, I'm talking about the following circuit: The inductor has a resistanse equal to the resistor in the circuit. So, the question is that, ...
5
votes
3answers
3k 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 ...
5
votes
1answer
175 views

If eddy currents are generated in superconductor what would happen if ..?

Eddy currents are generated in a conducting sheet when it oscillates in a uniform B field. It is stated in books that the sheet will show damping, as in the setup below: So, I want to ask if I placed ...
5
votes
1answer
401 views

Can I feel (the results of) electromagnetic induction from overhead rail lines in the human body?

A few weeks back, I was standing at a Hornsey rail station (in the UK) which uses overhead lines, and particularly has a number of parallel rail lines, all close to the platform. While I was standing ...
5
votes
0answers
1k views

How to calculate the energy transfer between working coil and working piece and dissipated energy of working piece in induction heating?

For who don't know how does induction heating work, a short description can be found here. However, my question is about physics. Assume I have a coil inductor calculated carefully 50 uH as below: ...
5
votes
4answers
452 views

Induction cooker + superconductive pot [closed]

What will happen if I put a super-conductive object on an induction cooker, and turn the cooker on?
5
votes
2answers
338 views

Faraday's law. And Faraday's law of induction

Can anyone properly tell me the difference between the two, and which one historically came first. A majority of sources directly connect "emf" to flux but the 'flux rule' isn't absolute. It isn't ...
4
votes
3answers
4k 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 ...