Hot answers tagged magnetic-fields
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Regarding rocky planets in our solar system:
Sure, you just have to go check out enough of the rocks on the surface.
Regarding exoplanets, and likely our own gas giants:
There are no methods by which we could determine such a thing with anything near today's technology. Maybe someday in the distant future we might be able to measure the magnetic field of ...
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If the Moon were exactly the same as the Earth, then sure, there is no major reason to suspect it would be any different. It is in the same orbit around the Sun as us, so it gets heated by the same amount. This would place it in the habitable zone.
However, habitability is not the same as being in the habitable zone, and the detailed answer depends on how ...
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Our two closest planetary neighbors -- Venus and Mars -- have no significant magnetic fields. In fact, the most recent numbers I know of for an Earth-like (dipole) field on Mars say that its strength as no more than 1/10000th the strength of Earth's. On the other hand, Jupiter's magnetic field is about 20000 times stronger than ours.
There is no reason ...
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Each electron has spin and it's own magnetic momentum, in sense each electron is just a very tiny magnet by it self, and there alignment makes there forces to be summed up, what makes a global one magnet, when electron mag. moments are chaotically aligned, the average sum is zero and your object will not behave as one big magnet.
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Less than g.
Since it generates energy in the conducting ring when passing through the ring, by conservation of energy, the magnet loses some kinetic energy (there are forces acting on the magnet.
See Lenz's law.
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I think that you are mistaking "one-sided" magnets and "unipolar" magnets.
...strictly one-sided magnet (generating no magnetic field whatsoever on one side) is impossible...
No. There is no problem in having a magnet with a field on one side. The hdd head is the example (here is a picture).
What you cannot have is a magnet with only one pole -- ...
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For future reference, if you even have only the most basic understanding of the physics behind it, you can guess that the fastest the mag field would drop off would be order $1\over r^2$. And you can guess that it originates from the center of Earth. Since we're sitting pretty at ~6371km, adding another 100-1000 km would not even decrease it by half, let ...
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I know that this doesn't directly answer your question about Purcell's reasoning (see addendum I wrote after reading Purcell's argument), but here's how a uniqueness proof would go.
Suppose that two fields $\mathbf B_1$ and $\mathbf B_2$ both satisfy the magnetostatics equations
$$
\nabla\times\mathbf B_i = \mu_0\mathbf J, \qquad \nabla\cdot\mathbf B_i = ...
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Moving charge always produces a magnetic field. If you have a non-zero current then you have non-zero moving charge and a magnetic field will be produced.
You can achieve essentially no magnetic field though by using two wires right next to each other each carrying current in the opposite directions. As long as the wires are very close and the amount of ...
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Magnetic surveys are used for prospecting for oil or minerals.
On top of the earth's magnetic field there are small contributions form magnetic materials in the surface rocks, especially granites.
You can use this to either find large bodies of volcanic rock that migth have minerals or diamonds - or alternatively you can find large volumes with no magnetic ...
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I believe that in that text, $i$ refers to the magnitude of the current (a scalar), which is assumed to be in the same direction as the length vector $\vec{L}$ (a vector).
There's no need for both $i$ and $\vec{L}$ to be vectors. Think of current flowing through a wire—if $i$ were a vector ($\vec{i}$), then the direction of $\vec{i}$ would always be the ...
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The basic physcs here is the Lorentz force on a moving charge, $q$, with velocity, $\vec{v}$ due to a magnetic field $\vec{B}$.
$$ F = q \left( \vec{E} + \vec{v} \times \vec{B} \right) \quad ,$$
where we ignore the electrical field so we get
$$ \vec{F}_B = q \vec{v} \times \vec{B}\quad .$$
The cross-product implies that the force acts perpendicularly to ...
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The essential physics this encodes is the superposition principle, which is at the heart of classical electromagnetic theory. What this states is that the fields from a collection of sources is the vector sum of the fields created by each different source. In particular this means that twice the currents generates twice the vector potential and twice the ...
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The simplest explanation I know of requires only one test charge and two reference frames with a relative velocity between them.
Frame 1: The charge is at rest. It is the source of a (purely) electric field.
Frame 2: The charge is moving. It is a current, and the source of a magnetic field.
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A Halbach array? Basically the magnetic domains are oriented in a pattern that produces the appearance of a strong magnetic field on one side and a significantly reduced magnetic field on the other side.
http://en.wikipedia.org/wiki/Halbach_array
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One simple approximation that you could make is to assume that the human body is made of water. Then you can reduce your question to: what happens to water molecules in a magnetic field. Consequently, you would have to ask how you can break the Van der Waals Bond in water with a magnetic field.
I think here you would have to differentiate between a static ...
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I'm only going to try to address the question of DC fields.
Medical MRI uses uniform fields of about 0.5 to 3.0 T. In a head MRI, the Lorentz force on ions in the brain can cause neurological effects such as vertigo. I've heard that this shows up in particular when the patient moves his head.
Here is a famous picture of a frog being levitated by a 16 T ...
3
There is one and only way to cancel something: add its negative to itself. However, there is an alternative to cancellation for shielding a region from external electromagnetic fields.
Generally speaking, methods of isolating a region from external electromagnetic fields (EM shielding) can be divided into two categories, passive and active. A passive shield ...
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David H provided a good answer, but the short answer to your question is "yes", other shielding (passive) exists. A Mu-Metal ($\mu {-metal}$) has a very high magnetic permeability and can be used to provide magnetic shielding. Some call these "Zero gauss chambers". These essentially "channel" the magnetic field around the center of the chamber.
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Just some pointers to get you started: The side length allows you to calculate the flux through a benzene ring given a magnetic field, which should then give you the induced current, if you claim that the electrons in the benzene ring are metallic (not a bad approximation due to their delocalized nature).
Another thing you can look at is this article on ...
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There isn't a mechanism. You're trying to find a mechanism for how two abstract objects can exchange identities. Any mechanism involving abstractions must consist of abstractions. So,the only way to explain it is through mathematics.
Least abstract way to look at it
I feel that the least abstract way to explain it is to look at two stationary charges. They ...
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When I was an undergrad, I was routinely subjected to magnetic fields thousands of times more powerful than Earth's because I was a research subject for MRI experiments. I noticed no powerful emotions induced by the magnetism, and I haven't heard of other subjects experiencing them, either. (People do experience claustrophobia in the MRI, but probably not ...
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The physical meaning is the length of electron trajectory along which this electron gains phase factor comparable with $2\pi$ from the magnetic field. Normally, it is rather large. When is is as small as lattice constant, it means that the magnetic field is comparable with electric field in the atom which is rather rare situation.
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Theoretically yes.
It would have to produce a magnetic field of sufficient strength of course.
The Earth's magnetic field at the Earth's surface ranges from 25 to 65 µT. Given that Mars is approximately 50% smaller than the Earth a smaller field would probably be sufficient.
The benefits of the shielding would be:
The level of radiation at the surface ...
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It doesn't have to be coiled. Magnetic fields will be created as long as you have a current through a wire.
Coiling may make the field strength stronger.
How strong the field strength is in practice also depends on the current through the wire and whether your power cable has shielding.
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why do we not get a shock?
Because the electric resistance of a human body is by orders of magnitude higher than the resistance of the steel pot.
why is it that current is converted to heat while it has a good conductor(say, steel) to flow through?
According to Maxwell–Faraday equation, changing magnetic field creates the electric field, i.e. the ...
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First, find the electric and magnetic fields generated by the individual wires. You have probably already done this if you are working on this problem, but if not, they are easy to find using a Gaussian surface and an Amperian loop:
$$ \oint \mathbf{E}\cdot d\mathbf{a} = \frac{Q_{enc}}{\epsilon_0} \quad\quad\quad\quad \oint \mathbf{B}\cdot d\mathbf{l} = ...
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The metal plates the magnets are glued to are an Iron and Nickel alloy that has a very high magnetic permeability called a Mu-metal.
I don't understand all of the details of magnetism or how Mu-metal works but that should get you started.
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I would guess the question is asking you to calculate the magnetic field that produces a force exactly equal to the gravitational force. That is, without the magnetic field the particle will accelerate downwards due to gravity. You need the field that exactly balances this to the particle carries on in a straight line.
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There were historically several systems of units (ancestors to modern SI, CGS electric, CGS magnetic, CGS Gaussian, CGS by Heaviside), and the ultimate choice in favour of Gaussian CGS was made when Special Relativity has united electric and magnetic fields into one electromagnetic field tensor. Only in Gaussian (and Heavisidian) versions, these fields take ...
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