# Tag Info

4

If you balance the forces due to the electric and the magnetic fields on the charged particle in such a way that there is no resultant force on the charged particle, then that is called a velocity selector. It means that the Lorentz force on the particle is 0. $$F =Q(E + v \times B) = 0$$ This allows you to measure the velocity of the charged particles ...

3

The words ultimately refer to the same "objects" but they describe different aspects of them. "Permanent magnets" are objects and they're defined by the external property (what they look like from outside) that the magnetic field remains nonzero around these objects without any activity. On the other hand, "ferromagnets" are materials and the focus is on ...

3

Notice the photons are reduced around the smaller one. Is that happening before the photon sphere? The photon sphere by definition does not send any photons in our direction, as it is a spherical region of space where gravity is strong enough that photons are forced to travel in orbits. So the photons seen come from the region before, ...

2

In a comment you say (I fixed a few words in this quote) "If it was a neutron star an atom would lose its electrons and protons before becoming a part of that star"... And in the question you say, "Are photons absorbed by atoms compressed out by gravity". This reminds me of Feynman's father. If you Google "feynman father photon", you should find the story ...

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The torque exerted by $\vec B$ is perpendicular to it, so the $z$ component of angular momentum is conserved.

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There is only one type of magnetic field, but there are multiple ways to generate a magnetic field. A bar magnet has a permanent magnetic field while a electromagnetic has a magnetic field only when the current is applied. Another way to get a magnetic field is to induce one. So you place an iron bar near one pole of a bar magnet but not touching. The bar ...

2

The formula is local, so it is correct for any geometry (I did not check your factors). To apply the formula to the case of a wire, you have to calculate the distribution of magnetic field in the wire depending on the distance from the axis (as far as I remember, the dependence is linear for uniform current distribution). Then you need to integrate the ...

2

Magnet is said to split into two parts when the magnetic circuit is broken.In your case if the magnet is partially broken there is a fringing flux in the air gap but most of the field lines pass through the low reluctance path,which in the above case is the unbroken part.And if there has to be fringing of flux there has to be two unlike poles nearby and ...

2

This is an answer to question 3 relating to simple motors and dynamos. A simple motor and a simple generator are one and the same thing When a current flows through the coil of a motor the coil rotates in a magnetic field and so the coil acts as a generator with the induced electromotive force (emf from Faraday’s Law) in the opposite direction to the ...

2

Let's assume the magnetic field vectors point in z-direction (or: let's call the direction the magnetic field vector points "z"). Then we have for the magnetic field: $$\vec{B} = \begin{pmatrix}0\\0\\B\end{pmatrix}$$ and for the speed of the electron: $$\vec{v} = \begin{pmatrix}v_x\\v_y\\v_z\end{pmatrix}$$ The Lorentz-force $\vec{F}$ due to a magnetic ...

1

You seem to be asking two things, could a black hole's magnetic fields cool nearby matter, and could this cooling produce cold fusion. But maybe we should first ask whether "cold fusion" is a real thing. Nuclei contain protons and neutrons held together by pions. Fusion is when two nuclei become one. The barrier to this happening, is the positive electric ...

1

First of all, try to imagine a simple MRI experiment with an perfectly homogeneous main magnetic field in the order of 1-3 T and an object to image that only contains protons of the same kind (i.e. the signal-baring protons are chemically all of the same kind in the object, i.e. there is only water in your object). When the object is brought into the main ...

1

As was mentioned before, MRI uses irradiation of radio-frequency waves to excite sample and produce a signal. A metal rod is basically a dipole antenna. Depending on its lengths it can absorb energy from the RF field, if the RF field satisfies a resonance condition (i.e. if (half) the wavelengths is comparable to the length of the rod.). Since the ...

1

There are many many misconceptions tied into knots in your question. Firstly, the electric force between two charges doesn't depend on just the distance between them and their charges, it also depends on their velocity. When charge A moves then its electric field is different, so the electric force charge B feels is different. This means you can't reason ...

1

Well you are right in expecting an effect on the wire every time there is a change in the field. The magnetic induction phenomenon will occur with changes in the magnetic flux through the solenoid, which depends both the intensity of the magnetic field and the time in which the change occurs. Now when you say "flip the magnetised wire" if you mean sudden ...

1

The electric field $\vec E$ is normal to the surface of a conductor in the limit that the conductivity is large, $\sigma\to\infty$. If the conductivity were infinite, any electric field would cause the internal charges to accelerate (i.e. feel a force) in the direction of the field, until the field (and the corresponding force) vanished. Conductivity has ...

1

To find the distribution of B-field inside the wire $B(r)$ just use Ampere's Law. Although there is an integration to do it is a very simple one. Once you knoe how the B-filed depends on the distance from the centre of the wire you need to do an integration (again a fairly straight forward one) to eventuate the energy stored.

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The field given by components $E_x = \cos(wt)$ and $E_y = \cos(wt-\pi/2) = \sin (wt)$ is always a rotating field, unless $w= 0$, and it will always have amplitude $$\sqrt{E_x^2 +E_y^2} = \sqrt{\cos^2(wt)+\sin^2(wt)} = 1.$$ If $w>0$, the field will rotate counterclockwise, whereas if $w < 0$, the field will rotate clockwise. If $w = 0$, the field ...

1

The addition of two simple harmonic motions at right angles to one another produces what is called a Lissajous figure. If search for Lissajous Figures Simulation you will find a number of simulators. Make the x and y frequencies the same and the phase difference 90 degrees and you get your circle produced. I have not found a good one but here are two ...

1

All macroscopic objects we observe are emergent from the underlying particle/atomic/molecular nature, which by the way follows quantum mechanical equations. a) The reason we see electric fields is fundamentally because electrons and protons have electric charge, which generates their electric field. There are many ways that electric fields can be ...

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Assuming this is a fairly large sheet, and that you are interested in an approximate method, you could use a small compass and mark the direction of the magnetic field at many places on a grid. From these directions you can draw field lines; and contours are perpendicular to the field lines. If that is not good enough for you, it's quite easy to write down ...

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So how can the same virtual photons give rise to 2 different properties? The photon is an elementary particle, and in the quantum field theoretical framework, an electromagnetic field exists in all (x,y,z,t) which has zero vacuum expectation value unless a photon exists there, the excitation of the field. What is the vacuum expectation value? It is the ...

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Yes there is. To me, the best way to understand this is through the idea of multipole expansion. You can even do this for an electrostatic potential --- and then, via the symmetry apparent with Maxwell equations, figure out a similar expansion for a magnetic (vector) potential. To see the derivation of a multipole expansion, you can consult Griffith's ...

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The important thing here is that a magnetic dipole, like a permanent magnetic or induced magnetism in ferrous material, produces a nonuniform field. The potential energy of a magnetic dipole $\vec\mu$ in a magnetic field $\vec B$ is $$U = -\nabla( \vec \mu \cdot \vec B).$$ Most frequently (as in anna v's answer) this is used to explain the torque which ...

1

This is actually an interesting question because you're asking about a solenoid rather than a simple wire. That means there are actually a few different things going on here. All of the electromagnetic signals at work here travel at $c$. The first thing to happen is, when you connect the battery at one end of the solenoid, current starts flowing in the ...

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