Quantum Locking

[BrotherJosh]

Hopefully, someone with more knowledge than myself could go in depth on this...pretty fascinating! If it's true The only thing I can think of is Flux Pinning.

[Noggy]

When a superconductor is very cold it allows an electric field in it that doesn't contain any energy. This is really weird. Because it is a static electric field, it repels the magnets on the stick the dude is holding. However, there are tiny imperfects in his superconducting disc. Because of this the magnetic field lines can poke through it in tiny places. Imagine it as if there were pieces of fishing line that came up through a small hole in the magnet. It is like that, but you can't see it.

[Noggy]

When a superconductor is very cold it allows an electric field in it that doesn't contain any energy. This is really weird. Because it is a static electric field, it repels the magnets on the stick the dude is holding. However, there are tiny imperfects in his superconducting disc. Because of this the magnetic field lines can poke through it in tiny places. Imagine it as if there were pieces of fishing line that came up through a small hole in the magnet. It is like that, but you can't see it.

 

I should say that because it has a constant electric field in it, that makes the entire sphere to be at the same potential. So, like a conductor, all of the charge will go to the surface. Because its a super conductor, the charges move freely along the surface because it doesn't take any work. This makes currents. Which cause magnetic fields. Just the right kind to cancel the magnetic field within the superconductor. Except for, in this case, the tiny imperfections in it that allow the fishing lines of magnetic field to go through.

[RankStranger]

Question for you, Noggy. I probably SHOULD know this... but it's never been clear to me. Are electric fields and magnetic fields pretty much the same thing? I know that they behave very similarly (if not identically), but they kinda come from different sources (at least on the level that I understand them).

 

I mean, I know that an electric field is generated by current flow. But you wrap that current flow around a chunk of iron, and you get an electromagnet. Which acts (best I can tell) just like a regular magnet until you turn it off. Are the fields the 'same thing'? Or just similar things?

[foolish girl]

 

Noggy, Thanks your explanation made it make more sense.

 

This video breaks it down a little bit with a diagram.

[Noggy]

Question for you, Noggy. I probably SHOULD know this... but it's never been clear to me. Are electric fields and magnetic fields pretty much the same thing? I know that they behave very similarly (if not identically), but they kinda come from different sources (at least on the level that I understand them).

 

I mean, I know that an electric field is generated by current flow. But you wrap that current flow around a chunk of iron, and you get an electromagnet. Which acts (best I can tell) just like a regular magnet until you turn it off. Are the fields the 'same thing'? Or just similar things?

 

No they are not the same thing. Also, an electric field is not generated by current flow. Current flow is a product of an electric field.

 

An electric field is made by charges. If something is charged, it creates a "field" throughout all space. If it is a positive charge, it it synonymous with lines going from the charge outwards from it at every point to every point in space. The electric field gets weaker (less dense lines) the farther you go out from the charge.

 

A magnetic field is a loop. There is no starting point and no endpoint. This is why there are no magnetic monopoles. The lines go out of the north end and loop back around inside the south end. You can see this quite clearly with iron filings and a bar magnetic.

 

However, the electric and magnetic field are linked to each other. A changing electric field (current that is changing) will create a magnetic field that is perpendicular to it. Like you said when you have a current through a wire, a magnetic field is formed around the wire. However, when you put the iron near it the magnetic field that is near the wire then MAGNETIZES the iron. So now you have something that is a magnet, rather than just a magnetic field around a wire.

 

It is important to note that a constant current will produce no magnetic field, because the electric field that drives the current (points from one end of the straight wire to the other) is static. Your electric field has to CHANGE in order to produce a magnetic field.

 

If you have a wire of current like so:

 

--------------------------------------------->

 

No magnetic field will be formed. However, if its an AC current, then the value of the current IS changing and you will give a magnetic field that is pointing perpendicular to the direction of the wire (that is, it is intersecting it at a 90 degree angle). It forms a "loop" around the wire.

 

You don't have to change the value of the current, however. You can just change the DIRECTION of the current. This is how an inductor works (which i figure you know what that is). Because the wire is looped, the current is CHANGING direction, and a magnetic field is created around the inductor.

 

Thats how the magnet-coil system works in your car, and in turbines. The steam (or whatever else) turns the turbine (which is a magnet), and you have a coil wrapped around it. This changes the direction of the magnetic field, which then puts a current into the coil that is wrapped around it. BOOM you just turned steam into electricity.

[paul34]

...

[MagickMonkey]

 

...

However, the electric and magnetic field are linked to each other. A changing electric field (current that is changing) will create a magnetic field that is perpendicular to it. Like you said when you have a current through a wire, a magnetic field is formed around the wire. However, when you put the iron near it the magnetic field that is near the wire then MAGNETIZES the iron. So now you have something that is a magnet, rather than just a magnetic field around a wire.

 

It is important to note that a constant current will produce no magnetic field, because the electric field that drives the current (points from one end of the straight wire to the other) is static. Your electric field has to CHANGE in order to produce a magnetic field.

 

If you have a wire of current like so:

 

--------------------------------------------->

 

No magnetic field will be formed. However, if its an AC current, then the value of the current IS changing and you will give a magnetic field that is pointing perpendicular to the direction of the wire (that is, it is intersecting it at a 90 degree angle). It forms a "loop" around the wire.

 

You don't have to change the value of the current, however. You can just change the DIRECTION of the current. This is how an inductor works (which i figure you know what that is). Because the wire is looped, the current is CHANGING direction, and a magnetic field is created around the inductor.

 

Thats how the magnet-coil system works in your car, and in turbines. The steam (or whatever else) turns the turbine (which is a magnet), and you have a coil wrapped around it. This changes the direction of the magnetic field, which then puts a current into the coil that is wrapped around it. BOOM you just turned steam into electricity.

 

Not quite correct. A constant current does produce a magnetic field. You need a changing magnetic field to induce a current in a piece of wire, which is why you need an alternating current in one side of a transformer to induce a current in the other side, but you still have a magnetic field with any current.

 

Check out this Youtube video with an electromagnet made using direct current.

 

 

Also, for electromagnets, you generally wouldn't want alternating current due to inductive reactance.

[RankStranger]

Thanks for the explanations- this clarifies things quite a bit.

 

I've studied both fields in physics classes- but it's entirely theoretical. Nothing hands-on. So while I can do the math and make the numbers come out right, that doesn't necessarily make the whole thing clear to me. Add in a Pakistani professor who barely speaks English and a large class size... and I can't say I really 'learned' a whole lot in that class.

 

But I think I get what ya'll are saying. When you say 'electric field', you really MEAN 'electric field'... as in the electric potential itself. As opposed to the magnetic field that can be generated by said electricity.

[sciencemike]

Thanks for the explanations- this clarifies things quite a bit.

 

I've studied both fields in physics classes- but it's entirely theoretical. Nothing hands-on. So while I can do the math and make the numbers come out right, that doesn't necessarily make the whole thing clear to me. Add in a Pakistani professor who barely speaks English and a large class size... and I can't say I really 'learned' a whole lot in that class.

 

But I think I get what ya'll are saying. When you say 'electric field', you really MEAN 'electric field'... as in the electric potential itself. As opposed to the magnetic field that can be generated by said electricity.

 

RS, you might find this web applet to be pretty cool:

 

http://www.falstad.com/circuit/

 

It has helped me understand how circuits operate on a more intuitive level. It's also really cool that you can build your own circuits and prototype them online, without ever even breaking out the soldering iron and (solderless-)breadboard!

 

Electromagnetism, as Noggy and MagickMonkey were saying, is based on four principle laws that make up Maxwell's Equations. I'll explain them in the manner that makes the most sense to me, it is a compilation of what I've learned from multiple textbooks on the subject (not of all I think explain them too well). Note this is a little mathy but try to bear with me

 

Gauss' Law: ∇·E=(ρ/ε0). The quantity on the LHS is the "divergence of the electric field" although it is physically interpreted as the rate of change of the electric field itself as it "diverges" away from a source. The terms above, the ∇ is the del operator which represents the mathematical quantity of divergence. In cartesian coordinates, this equates to ∇=dF/dx+dF/dy+dF/dz. E is the electric field, ρ is the charge density, and ε0 is a constant known as the "Permittivity of Free Space" and is a universal constant. Notice that when written this way the quantities on the RHS are "source" terms. This is important because when we look at the analogous laws for magnetic fields, there is no source (that is, there are no magnetic monopoles).

 

A better way to see this is to look at the integral form of this equation:

 

∫ E·da = (1/ε0) ∫ ρ dV

 

where da is the surface area, and the ∫ integrals are either surface (da) or volumetric (dV) integrals.

 

When written this way, the change in the electric field (that is, the difference in the electric field flux from some r to r+dr) is equal to how much the electric field shrinks in volume dV. A similar analogy is used in fluid mechanics to describe a similar scenario. Suppose we had a sphere of water of radius R and we "explode" the sphere by a little bit so the radius is now R+dR. The mass of water leaving the original sphere of radius R is equal to the mass of water in dV leaving the sphere. This similar analogy can also be applied to electric fields.

 

Faraday's Law: ∇xE=-dB/dt. The quantity on the LHS refers to the curl and conceptually refers to the rotational rate of change of the electric field. The right hand side shows a time-dependent magnetic field (dB/dt). Physically, this means that a changing magnetic field can induce an electric field. It can be also written in integral form as:

 

Φ = ∫ E·dl = -∫ (dB/dt) da

 

where fancy phi Φ is the electromotive force (not a force in the traditional sense, this is a byproduct of traditional nomenclature) which has units of electric potential (Volts). The integral on the LHS is a line integral (you can somewhat think of this as a wire that gains an electric field through the motion of a moving magnetic field nearby).

 

Solenoidal Magnetic Law (this one has varying names): ∇·B=0. This law is similar to Gauss' law, only for magnetic fields. However, the RHS is zero, indicating that there is no "source" term for magnets. In our water sphere scenario, this would mean that there is no change in the mass of water leaving the sphere. This doesn't really make sense because the physics of mass transfer is very different than the physics of magnetic fields. Lets think of it slightly differently: Suppose our water sphere is now just a spherical magnet with field lines expanding outward in all directions. The sum of these magnetic field lines is the same on the inside as it is on the outside, as shown in the integral form:

 

∫ B·da = 0

 

Another way to think of this is water flowing from an infinite reservoir where the total amount of water flowing doesn't really matter as much as the rate entering and leaving the volume being the same.

 

Ampere's Law: ∇xB-(μ0*ε0)*(dE/dt)=μ0*J. This equation, like Faraday's Law, links the magnetic fields to the electric fields. The "source" term on the RHS is the induced current J, while the left hand side relates the changing electric and magnetic fields. Note that the curl operator changes the magnetic field perpendicularly to the electric field (this has important consequences with the propagation of light in particular). Physically, this law states that a changing electric field induces a magnetic field.

 

In integral form, this is written as:

 

∫ B·dl = μ0*Jenc + (μ0*ε0)*[ ∫ (dE/dt) da ]

 

Where the first term, ∫ B·dl is the change in magnetic field from l to l+dl, μ0*Jenc is our current from the electric field that drives the magnetic field, and ∫ (dE/dt) da is the rate of electric field change in a given surface area.

 

Maxwell's equations are elegant, but at the same time they are extremely dense and it takes a lot of exposure to it to really feel comfortable with the physical meaning of each of these laws. Hopefully this will help everyone here as much as it helped me (it was helpful to review it every once in a while).

[MagickMonkey]

Thanks for the explanations- this clarifies things quite a bit.

 

I've studied both fields in physics classes- but it's entirely theoretical. Nothing hands-on. So while I can do the math and make the numbers come out right, that doesn't necessarily make the whole thing clear to me. Add in a Pakistani professor who barely speaks English and a large class size... and I can't say I really 'learned' a whole lot in that class.

 

But I think I get what ya'll are saying. When you say 'electric field', you really MEAN 'electric field'... as in the electric potential itself. As opposed to the magnetic field that can be generated by said electricity.

 

RS, you might find this web applet to be pretty cool:

 

http://www.falstad.com/circuit/

 

It has helped me understand how circuits operate on a more intuitive level. It's also really cool that you can build your own circuits and prototype them online, without ever even breaking out the soldering iron and (solderless-)breadboard!

 

Electromagnetism, as Noggy and MagickMonkey were saying, is based on four principle laws that make up Maxwell's Equations. I'll explain them in the manner that makes the most sense to me, it is a compilation of what I've learned from multiple textbooks on the subject (not of all I think explain them too well). Note this is a little mathy but try to bear with me

 

Gauss' Law: ∇·E=(ρ/ε0). The quantity on the LHS is the "divergence of the electric field" although it is physically interpreted as the rate of change of the electric field itself as it "diverges" away from a source. The terms above, the ∇ is the del operator which represents the mathematical quantity of divergence. In cartesian coordinates, this equates to ∇=dF/dx+dF/dy+dF/dz. E is the electric field, ρ is the charge density, and ε0 is a constant known as the "Permittivity of Free Space" and is a universal constant. Notice that when written this way the quantities on the RHS are "source" terms. This is important because when we look at the analogous laws for magnetic fields, there is no source (that is, there are no magnetic monopoles).

 

A better way to see this is to look at the integral form of this equation:

 

∫ E·da = (1/ε0) ∫ ρ dV

 

where da is the surface area, and the ∫ integrals are either surface (da) or volumetric (dV) integrals.

 

When written this way, the change in the electric field (that is, the difference in the electric field flux from some r to r+dr) is equal to how much the electric field shrinks in volume dV. A similar analogy is used in fluid mechanics to describe a similar scenario. Suppose we had a sphere of water of radius R and we "explode" the sphere by a little bit so the radius is now R+dR. The mass of water leaving the original sphere of radius R is equal to the mass of water in dV leaving the sphere. This similar analogy can also be applied to electric fields.

 

Faraday's Law: ∇xE=-dB/dt. The quantity on the LHS refers to the curl and conceptually refers to the rotational rate of change of the electric field. The right hand side shows a time-dependent magnetic field (dB/dt). Physically, this means that a changing magnetic field can induce an electric field. It can be also written in integral form as:

 

Φ = ∫ E·dl = -∫ (dB/dt) da

 

where fancy phi Φ is the electromotive force (not a force in the traditional sense, this is a byproduct of traditional nomenclature) which has units of electric potential (Volts). The integral on the LHS is a line integral (you can somewhat think of this as a wire that gains an electric field through the motion of a moving magnetic field nearby).

 

Solenoidal Magnetic Law (this one has varying names): ∇·B=0. This law is similar to Gauss' law, only for magnetic fields. However, the RHS is zero, indicating that there is no "source" term for magnets. In our water sphere scenario, this would mean that there is no change in the mass of water leaving the sphere. This doesn't really make sense because the physics of mass transfer is very different than the physics of magnetic fields. Lets think of it slightly differently: Suppose our water sphere is now just a spherical magnet with field lines expanding outward in all directions. The sum of these magnetic field lines is the same on the inside as it is on the outside, as shown in the integral form:

 

∫ B·da = 0

 

Another way to think of this is water flowing from an infinite reservoir where the total amount of water flowing doesn't really matter as much as the rate entering and leaving the volume being the same.

 

Ampere's Law: ∇xB-(μ0*ε0)*(dE/dt)=μ0*J. This equation, like Faraday's Law, links the magnetic fields to the electric fields. The "source" term on the RHS is the induced current J, while the left hand side relates the changing electric and magnetic fields. Note that the curl operator changes the magnetic field perpendicularly to the electric field (this has important consequences with the propagation of light in particular). Physically, this law states that a changing electric field induces a magnetic field.

 

In integral form, this is written as:

 

∫ B·dl = μ0*Jenc + (μ0*ε0)*[ ∫ (dE/dt) da ]

 

Where the first term, ∫ B·dl is the change in magnetic field from l to l+dl, μ0*Jenc is our current from the electric field that drives the magnetic field, and ∫ (dE/dt) da is the rate of electric field change in a given surface area.

 

Maxwell's equations are elegant, but at the same time they are extremely dense and it takes a lot of exposure to it to really feel comfortable with the physical meaning of each of these laws. Hopefully this will help everyone here as much as it helped me (it was helpful to review it every once in a while).

 

Multisim Student Edition is also a great cheap ($40) way to do circuit simulations. When I have more time (I'm short on that these days), I'll look more into what you just said. I think I might have taken enough math to digest some of that.

[Ouroboros]

Hopefully, someone with more knowledge than myself could go in depth on this...pretty fascinating! If it's true The only thing I can think of is Flux Pinning.

How can he touch it? Isn't it frozen with liquid nitrogen and extremely cold? And how is that gravity as a force doesn't affect it, but the force from the hand moving it does affect it?

 

---

 

One of their other videos show in more detail how they built it:

[RankStranger]

Thanks, Mike- I'll have a look. Thing is that I have little problem grasping electronic circuits on an intuitive level. It's understanding them on a theoretical/analytical level that I have a hard time with.

 

And that's one reason why I'm majoring in mechanical engineering rather than electrical.

 

And I'll agree with MM about multisim. I have a ripped-off version (software like that is all over the bittorrent sites). Comes in really handy for throwing an idea together and testing it.

[Noggy]

 

How can he touch it? Isn't it frozen with liquid nitrogen and extremely cold? And how is that gravity as a force doesn't affect it, but the force from the hand moving it does affect it?

 

 

I've touched stuff that is cold as liquid nitrogen. It's not really a problem unless you keep your finger on htere for awhile.

 

And gravity DOES effect it, thats why it is in equilibrium and not just flying straight up forever. Your finger knocks it off of equilibrium. also, your finger is a lot more powerful than gravity on that little disc.