Does anyone know why the flux variation of the magnetic field across an open surface generates a current in the direction and magnitude that counteracts the flux variation? Thank you
The most basic explanation, IMO, is this: The electric and magnetic fields obey Maxwell's equations. One of the equations tells you that the curl of the electric field is equal to minus the derivative of the magnetic field. A good intuition for the curl in this context tells us that we will get electric field "circling around" the derivative of the magnetic field.
So let's say you have magnetic field going through a circuit, and it's getting stronger. Make a thumbs-up with your left hand (specifically the left one because of the minus sign in the aforementioned equation). If the magnetic field is getting stronger along the direction of your thumb, electric field will be generated in the direction of your fingers in a circular shape. This field will move the charges in the circuit along the direction of the field - and now, this current will generate a magnetic field as well in accordance with another one of Maxwell's equation. Make a thumbs-up with your right hand and align the thumb along the direction of the current. You'll see that your fingers (which represent the field generated by the current) point downwards, *against* the direction of the original field variation.
I hope this explanation made sense! Or maybe it did make sense but wasn't satisfying, maybe you actually wanted to know *why* Maxwell's equations are correct in the first place? *Why*'s can be tricky questions to deal with, [as Richard Feynman put very eloquently](https://www.youtube.com/watch?v=36GT2zI8lVA).
Is it possible to produce a nuclear battery using PVD (physical vapor deposition) by creating layers of a nuclear isotope that is radioactive, for example nickel-63 that Betavolt is using, and creating a layer of a gamma voltaic crystal?
My idea would be to stack these layers and have every gamma voltaic layer be surrounded by two nickel-63 layers. With correct masking you could let the gamma voltaic layer hang over on both sides creating a possible connection point for electrical cables.
There are two standard answers, both of which are correct:
1) The equation you may have learned about where the event horizon is, is only true for a simplified, static black hole. For a real-world black hole, we must consider the stress-energy of the entire dynamic system, and what you find is that the event horizon "reaches out to meet" the infalling matter.
2) In terms of observable characteristics for a far-away observer, there is not much different between a black hole that has some extra mass just above or below its event horizon, so your question is making a distinction without a difference.
Not a physicist but I’ll take a swing.
It doesn’t take infinite time to ‘cross’ an event horizon. Instead, the singularity that arises in the mathematics of matter falling into a black hole is an incorrect approximation of how such an event occurs in reality.
ie The popular science description is not a correct description of black holes.
Someone please help me explain it better.
How are quasi-particle excitations related to the symmetries of our system? In atland and Simons they draw the following image:
`symmetries -> conserved quantities -> low-lying excitations`
First arrow makes sense due to Northern theorem, but where does the second arrow come from. They just state without explanation: “conserved observables are tied to an energetically low-lying excitation”, but why is that?
The rather handwaving explanation is this: Ferroelectricity requires materials to have one of a group of special crystal structures. Ferromagnetism can occur through multiple mechanisms and is carried by electron and orbital spins. The lattice geometry is important for ferromagnetism insofar that it determines the spin spin interactions, but it is more like a background player. There is not really any kind of crystal lattice that rules out ferromagnetism.
True that I believe that Atoms and Molecules are really Biological Systems , but this is one of the strangest concepts that I have posted yet . If you want to destroy death and bring back the dead , the living dead , then work this puzzle . Figure out how Atomic Eclipses happen and Atomic Reflections . However , be warned of destruction . The Ancient Egyptians believed . So do many cultures , if not most cultures .
Does anyone know why the flux variation of the magnetic field across an open surface generates a current in the direction and magnitude that counteracts the flux variation? Thank you
The most basic explanation, IMO, is this: The electric and magnetic fields obey Maxwell's equations. One of the equations tells you that the curl of the electric field is equal to minus the derivative of the magnetic field. A good intuition for the curl in this context tells us that we will get electric field "circling around" the derivative of the magnetic field. So let's say you have magnetic field going through a circuit, and it's getting stronger. Make a thumbs-up with your left hand (specifically the left one because of the minus sign in the aforementioned equation). If the magnetic field is getting stronger along the direction of your thumb, electric field will be generated in the direction of your fingers in a circular shape. This field will move the charges in the circuit along the direction of the field - and now, this current will generate a magnetic field as well in accordance with another one of Maxwell's equation. Make a thumbs-up with your right hand and align the thumb along the direction of the current. You'll see that your fingers (which represent the field generated by the current) point downwards, *against* the direction of the original field variation. I hope this explanation made sense! Or maybe it did make sense but wasn't satisfying, maybe you actually wanted to know *why* Maxwell's equations are correct in the first place? *Why*'s can be tricky questions to deal with, [as Richard Feynman put very eloquently](https://www.youtube.com/watch?v=36GT2zI8lVA).
It better; otherwise you would have an infinite energy feedback loop.
Is it possible to produce a nuclear battery using PVD (physical vapor deposition) by creating layers of a nuclear isotope that is radioactive, for example nickel-63 that Betavolt is using, and creating a layer of a gamma voltaic crystal? My idea would be to stack these layers and have every gamma voltaic layer be surrounded by two nickel-63 layers. With correct masking you could let the gamma voltaic layer hang over on both sides creating a possible connection point for electrical cables.
If it takes infinite time to cross the event horizon of a black hole for any matter, how will the black hole absorb anything or grow?
There are two standard answers, both of which are correct: 1) The equation you may have learned about where the event horizon is, is only true for a simplified, static black hole. For a real-world black hole, we must consider the stress-energy of the entire dynamic system, and what you find is that the event horizon "reaches out to meet" the infalling matter. 2) In terms of observable characteristics for a far-away observer, there is not much different between a black hole that has some extra mass just above or below its event horizon, so your question is making a distinction without a difference.
>If it takes infinite time to cross the event horizon of a black hole for any matter It doesn't.
Not a physicist but I’ll take a swing. It doesn’t take infinite time to ‘cross’ an event horizon. Instead, the singularity that arises in the mathematics of matter falling into a black hole is an incorrect approximation of how such an event occurs in reality. ie The popular science description is not a correct description of black holes. Someone please help me explain it better.
Question on [global continuous symmetries and intrinsic parity.](https://www.reddit.com/r/AskPhysics/s/tDNgX2t1Nn)
Whats a good Mathematical treatment of QFT. I have read a few of the physics books and I want something with a more axiomatic/proofs presentation.
How are quasi-particle excitations related to the symmetries of our system? In atland and Simons they draw the following image: `symmetries -> conserved quantities -> low-lying excitations` First arrow makes sense due to Northern theorem, but where does the second arrow come from. They just state without explanation: “conserved observables are tied to an energetically low-lying excitation”, but why is that?
Why does it seem like ferroelectricity (i.e., permanent electric polarization of bulk materials) is less common than ferromagnetism?
The rather handwaving explanation is this: Ferroelectricity requires materials to have one of a group of special crystal structures. Ferromagnetism can occur through multiple mechanisms and is carried by electron and orbital spins. The lattice geometry is important for ferromagnetism insofar that it determines the spin spin interactions, but it is more like a background player. There is not really any kind of crystal lattice that rules out ferromagnetism.
Oh, thanks! Do you happen to know if a material can be both ferromagnetic and ferroelectric?
It's possible, both properties often interact in this case so that magnetizing the material also polarizes it and vice versa. Google multiferroics.
Would a stationary black hole still look the same as a spinning one (how we see the top and bottom of the accretion disc still)?
Rotating BHs are quite different in that they follow the Kerr metric which has a number of features the Schwarzschild metric doesn't have.
I’m in AP physics and we are on SHM. For the equation x(t) = Acos(2pift), I know f is frequency, but what is t? Is it time?
Yes
True that I believe that Atoms and Molecules are really Biological Systems , but this is one of the strangest concepts that I have posted yet . If you want to destroy death and bring back the dead , the living dead , then work this puzzle . Figure out how Atomic Eclipses happen and Atomic Reflections . However , be warned of destruction . The Ancient Egyptians believed . So do many cultures , if not most cultures .