The question is slightly deceiving however still simple for those academics therefore, here I present my question:  If I take a para-magnetic material and put it very close to a homogeneous magnetic field, the para magnetic material will start to accelerate towards the magnetic body thus it has kinetic energy (but I ensure it does not hit the magnet and stop it with my fingers) so does the magnetic field or body loose it magnetism or will the same magnetism stay? Because in Wikipedia, it says:     Energy is needed to generate a magnetic field both to work against the   electric field that a changing magnetic field creates and to change   the magnetization of any material within the magnetic field   However I'm sure that para-magnetic materials are not magnetized, so where is this energy coming from? Or is my understanding wrong if so can someone link me to a good website which uses mathematics and theory to show how para magnetic material works?  Thanks!
122090
I recently bought some , considered to be the world's best selling desk toy. Essentially, they are little, spherical magnets that can form interesting shapes when a bunch of them are used together.  After playing around with these buckyballs for a while, I wondered: "Can these guys ever lose their magnetism?" Then I went a step further and thought, "How are magnets affected by the 2nd law of thermodynamics?"  So, how are magnets affected by the 2nd law of thermodynamics? Do they break down and lose their magnetism over time (like iron rusts over time)?
25007
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 electromagnetic field. If you twist that wire into a coil then you can concentrate that field. You can then induce current into a different coil by placing it inside of the electromagnetic field created by the first coil.  So here are my questions:  Q1. Does the electromagnetic field contain any energy?  EDITED QUESTION  Q2. Electromagnetic fields are the same as waves, so does that mean that when current is induced, they get the energy from electromagnetic waves being exchanged, or do they induce current directly from the electromagnetic field?   Q3. If electromagnetic fields and waves are the same, then doesn't that mean that you can induce current from waves? Therefore transferring electricity over long distances?  Q4. What spectrum of light are the electromagnetic waves that are in a field created by electricity?  Q5. Finally, why is it not possible to induce current from the Earth's magnetic field? I thought Maxwell said that electric fields and magnetic fields were the same thing.   Thank you to anyone who answers.  Edited Q2: So my original question (although asked poorly) still stands. Where does the current that gets induced in the secondary coil come from? How does the electricity transfer from the primary coil to the secondary? For example, is it taken from the stored energy in the e.m field? Does the field just act as a bridge between the 2 coils? Or do the 2 coils exchange e.m waves which carry the electricity that is being transferred from coil 1 to coil 2? Or is it none of these things and something completely different?
77972
So I learned that the bar magnet makes a magnetic field and the field lines have a certain shape which kinda resembles 2 semi-ovals.  And if we pass current through a conductor then it makes a  magnetic fields and the field lines are in the form of concentric circles around the conductor.  My question is- why? Why do magnetic field lines take the shape that they take? There must be a reason behind it. Why aren't the field lines of a normal bar magnet shaped like the field lines of a conductor carrying electricity? And vice-versa?   Please explain it to me..i know that it delves very deep into the fundamentals of the working of science but still...please tell me the reason if anyone knows it
8392
In very recent publications, two groups in Maryland  and Harvard  have separately worked on constructing  following the path paved by the previous works of Norman Yao (e.g.  ). For example Chris Monroe et al. (Maryland) have realised (or claim to have) a time crystal by entangling the electron spins of a set of ytterbium ions while keeping the system out of equilibrium by alternately hitting the ions by a laser (to apparently create an effective magnetic field) and by another laser to flip their spins, in a repetitive manner.   Now time crystals have been previously theoretically predicted to exist  and , representing an out-of-equilibrium form of matter, in contrast to the commonly well known equilibrium forms of matter (solid, gas, liquids, liquid crystals...). So it is really great to see such works emerging and the field gaining steam on an experimental level.   That said, admittedly, it is very difficult to grasp these works for someone not involved in the field, but it would be incredibly valuable if, briefly, just the idea of time crystals could be explained at a conceptual level.  As in, what qualifies them as a new form of matter? Surely this form is dependent on some external drive to be kept out of equilibrium, right?   Which then begs to ask "how can it be a naturally occurring form of matter". On the other hand, what does it have in common with the usual concept of crystals, whose whole structure can be represented by spatially replicating the unit cell.  Is the time crystal an addendum to the latter by extending its spatial symmetry to also include a time symmetry?    This is merely an attempt to get more input in order to understand some of the main ideas involved in the original works of Frank Wilczek and Norman Yao. These new experimental realizations (see first paragraph) are very exciting to find out about.
114264
This is from my textbook, it is not an assigned problem, but I want to understand.   It says:      Consider the situation in the figure, in which there is a uniform electric field in the x direction and a uniform magnetic field in the y direction. For each example of a proton at rest or moving in the x, y, or z direction, what is the direction of the net electric and magnetic force on the proton at this instant?   I believe I need to use the equation   $$ F_{net}=(q\overrightarrow{E})+q(\overrightarrow{v} \times \overrightarrow{B}) $$  But I'm not sure exactly how. We've just started to learn about this, and I want to get a head start. Could anyone put me on the right track?
124191
is a question about the canonical momentum that I had asked some days ago, but I still have one point that I am not understand.  Considering a particle moves in a magnetic field with charge $q$ and mass $m$, its hamiltonian is $$H=\frac{\vec{P}^2}{2m}=\frac{(\vec{p}+q\vec{A})^2}{2m}$$ where $\vec{p}$ is the momentum of the particle, $\vec{A}$ is the vector potential of the magnetic field and $\vec{P}$ is the canonical momentum of the particle.  I think, because of the expression of the hamiltonian, the canonical momentum $\vec{P}$ is a conserved quantity.  But by the answer in , it seems that the canonical momentum is not conserved even in a simple example that a particle moves in a homogeneous magnetic field.  I am confused about this question. Is the canonical momentum conserved when a particle moves in magnetic field?
17853
Recently, I  was pondering over the thought that is most of the elementary particles have intrinsic magnetism, then can gravity be just a weaker form of electromagnetic attraction? But decided the idea was silly.    But I then googled it and found  article. Is this idea really compatible with other theories as the article mentions? Is there any chance of this proposition being true?
46827
I'm struck with two competing ideas on the question in the title.  :   How far can a magnetic field bend light?   A: Unfortunately, the path light takes is not affected by the presence of a magnetic field. Light itself is composed of an oscillating electric and magnetic field, and one very important property of electric and magnetic fields is what we call linearity. That is, if you have two sources of electric and/or magnetic fields, you can predict what the combined field is just by adding the two source fields together. The two fields don’t change each other at all.   (Answer #1)    Does electric charge affect the space time fabric? If so, why?    A: [See link. Rather, see both links if you must.]  I'm more inclined to consider the latter question and answer as the correct interpretation. Anyway, if anyone could help me out with this conceptualization that would be great, thanks.
33385
When I searched the net about magnetic field lines,  told something about contour lines and that magnetic materials placed along a magnetic field has some specific loci, which i did not understand. Can someone explain it to me in details.  Also how do we know that tangent to a magnetic field line gives the direction of magnetic field? I am very confused.
42570
We are always introduced to magnets by pictures illustrating a parallepiped magnet, a horseshoe magnet, etc... Anyway the first time we actually calculate a magnetic field is for eelectromagnets. Indeed I've rarely seen explaining or calculating the magnetic field of a permanent magnet. I know formulas for the magnetic field of a moving charge, around a conductive wire, inside a solenoid, but I don't have idea on how to go about calcualting the filed of a simple permanent magnet. It's like that without the help of electricity I'm stuck. I'd guess it would be heavily dependent on the magnetic material, its shape and the medium in which is placed. I hope that someone would provide me some insights on why such formulas are  never introduced in most physics courses and lay down some examples of a permanent magnet field caluclation.
70630
Basically, which is the correct formula for thermal energy, and is this the same as kinetic energy? My notes are pretty conflicting on this topic, and I'm getting pretty confused.
85027
This has been bugging me for a long time. Take  for example.  I have always thought that electricity will take the shortest path. When the electromagnet's windings are uninsulated, it seems that the electricity would flow straight through the "mass of metal" created by the wire, not in the circular path needed for the electromagnet to work. I have also seen solenoids that work like this. How does this design work?
68843
If I was to take a bunch of magnets and arrange them in a sphere (And keep them there with glue or plastic or something) so that the north pole faces the outside of the sphere and the south pole faces the inside, would the magnet have the same pole no matter what way I turn it or would the magnet be neutralized or something.  I'm envisioning a sphere made of magnets so that no matter what way I turn it it is always the same pole and that a bunch of these repelling each other would be really cool, is this possible?  In effect would this create a monopole magnet?
62329
I seem to have encountered a contradiction when thinking about the directions of $\textbf{H}$ and $\textbf{B}$ inside and outside a bar magnet.  Suppose that a bar magnet has a roughly constant magnetisation M pointing along the positive z direction. Suppose also that the magnet is made from an isotropic material, i.e. $\textbf{M}=\chi_m \textbf{H}$ (1). Therefore $\textbf{H}$ should be pointing in the same direction as $\textbf{M}$, provided that $\chi_m$ is positive, which should be the case for most magnetic materials? From the definition $\textbf{H}=\frac{1}{\mu_0}\textbf{B}-\textbf{M}$ and substituting using (1), we get $\textbf{B}=\mu_0(1+\chi_m)\textbf{H}=\frac{\mu_0(1+\chi_m)}{\chi_m}\textbf{M}=\frac{\mu_0\mu_r}{\mu_r-1}\textbf{M}$. Unless $\mu_r$ is less than 1, $\textbf{B}$ should also be parallel to $\textbf{M}$. Therefore so far we get that both $\textbf{H}$ and $\textbf{B}$ should point in the same direction as direction as $\textbf{M}$ inside the magnet, that is along the positive z direction.  We know that $\nabla\cdot\textbf{B}=0$ and thus applying boundary conditions on the top and bottom surfaces of the magnet (normal to the z axis) using an infinitesimally thin gaussian pillbox, we get that $\textbf{B}^\perp_\textrm{outside}=\textbf{B}^\perp_\textrm{inside}$. Therefore $\textbf{B}$ immediately outside the top surface should also point in the positive z direction. Assuming that there are no free currents near the magnet, $\nabla\times\textbf{H}=\textbf{J}_\textrm{free}=\textbf{0}$. Applying boundary conditions to the side surfaces of the magnet (parallel to the z axis), $\textbf{H}^\parallel_\textrm{outside}=\textbf{H}^\parallel_\textrm{inside}$. Therefore $\textbf{H}$ immediately outside the side surfaces must also point along the positive z direction. However, the field lines must also curl around and meet the top surface of the magnet, where $\textbf{H}$ will therefore need to point in the negative z direction. Since $\textbf{M}=\textbf{0}$ outside, $\textbf{H}=\frac{1}{\mu_0}\textbf{B}-\textbf{M}=\frac{1}{\mu_0}\textbf{B}$ and $\textbf{H}$ needs to be parallel to $\textbf{B}$ but we just argued that they point in opposite directions due to the boundary conditions. How do we resolve this contradiction?
95455
"Now we turn our attention to what happens in $S'$, in which the particle is at rest and the wire is running past (toward the left in the figure) with the speed $v$. The positive charges moving with the wire will make some magnetic field $\ B'$ at the particle. But the particle is now at $rest$, so there is no magnetic force on it! If there is no magnetic force on the particle, it must come from an electric field. It must be that the moving wire has produced an electric field. But it can do that only if it appears $charged$-it must be that a neutral wire with a current appears to be charged when set in motion."  So i got this from Feynman's lectures in physics volume 2 pg 13-7 and 13-8. I find it hard to believe that the particle experiences no magnetic force due to the moving wire although it's stationary. Since this is classical and not quantum electrodynamics if we assume the charged particle to have inertia, then by Newton's second law, the particle will remain at rest until acted upon by an external force, which i assume is the $magnetic$ $wind$ created by the moving wire past the stationary charged particle. Could someone please clarify??
8966
Suppose a moving proton traverses a uniform magnetic field with constant velocity. Note that because the proton is moving, it is generating its own magnetic field.   Is the magnetic force experienced by the proton completely explained by the Lorentz force law, i.e., F = q (v x B)?   Or, is the proton also experiencing an additional magnetic force arising from the interaction of its own magnetic field with the external field? If that is incorrect, is the Lorentz force law actually just describing the result of proton field-external field interactions, such that any and all magnetic force on the proton is explained by the Lorentz force?
106968
Frequently when EM waves are taught, it is said that the change in electric field causes a change in the magnetic field, which then causes a change in the electric field, and so on and so forth.   But from my understanding of basic electromagnetics, it is not necessarily a changing electric field that creates a change in magnetic field, but instead an accelerating charge. and it is this charge that creates both the electric and magnetic field. Again, from my understanding, a changing magnetic field is not generated by a changing electric field, but instead just happens to always be present perpendicular to a changing electric field due to the laws of electromagnetism.   Am I wrong? Or is the "mutual generation" concept between the electric and magnetic components of an EM wave an actual thing?