中午吃什么不会胖
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Results tagged with electromagnetism
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user 207910
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The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.
0
votes
Can electricity be induced only by a magnetic field?
I just learned that Magnetism is just electrostatics observed from a
different reference point.
No: that is not quite true. It is true that there are some simple situations in which there is a magne …
- 65.5k
1
vote
Accepted
If electromagnetic wave traval in straight line, how can it be like wavefronts spreading out...
Imagine two circles spreading out from two nearby centres. The circles spread out in a circular fashion, but the two points where they intersect both move in a straight line.
Now process that thought, …
- 65.5k
9
votes
Accepted
Alike charges can attract?
You have calculated the magnetic contribution to the force in the case where $\vec{v}$ is perpendicular to $\vec{r}$ (incidentally this is not the case for the configuration you described, but it can …
- 65.5k
0
votes
Magnetic fields inside hollow magnets, are the poles reversed?
We use the fact that magnetic field $B$ can be seen as arising from a collection of dipoles, and a permanent magnet can be seen as a collection of dipoles all aligned.
Consider the following pattern:
…
- 65.5k
1
vote
Accepted
Why is the time derivative of the magnetic field finite?
Physically $dB/dt$ is finite.
But one might be interested in a case where $dB/dt$ is large enough that it cannot be neglected on the distance scale associated with an interface, such as for example th …
- 65.5k
1
vote
The right hand rule confusion?
Electric and magnetic fields are best understood using the terminology "electric field ${\bf E}$" and "magnetic field $\bf B$". In the case of a magnetic field this is better terminology than "lines o …
- 65.5k
1
vote
How do I find the direction of current with Flemming's left hand rule?
I am going to answer by encouraging you to use your right hand rather than your left hand. The reason is that to do all of physics and mathematics it is sufficient to only use right hand rules. Introd …
- 65.5k
2
votes
Accepted
How does portion of a field get separated when charge is accelerated?
For a full answer you just need to keep reading the book.
Ultimately there is just one electromagnetic field filling the entire universe. It is continuous. No part of it is detached from any other par …
- 65.5k
0
votes
How does a magnet cause magnetic force and its magnitude/direction?
In physics there are chains of reasoning. These chains seek to uncover the causes of given effects, and to "unpack" the complex mechanism or structure which combines together to produce given results. …
- 65.5k
0
votes
Why does nature “abhor” a change in flux?
It's a handy way of remembering a property of magnetic behaviour which is a bit like Newton's first law. Magnetic flux does not decay away, nor grow, just on its own. It stays constant unless there is …
- 65.5k
1
vote
Largest item experiencing electromagnetic forces that are stronger than gravity
"what are the largest objects ever to experience an electromagnetic force stronger than the gravitational force"
Answer is: everything except black holes and neutron stars.
That is, the internal in …
- 65.5k
1
vote
Accepted
What happens to a compass below an AC line?
Your use of the phrase "cancel out" and the answer "too fast" are two ways of saying the same thing, but both are a bit vague and unclear.
The force from the oscillating $B$ field at time $t$ is in th …
- 65.5k
3
votes
Does stacking two magnets together increase the magnetic strength?
Yes, stacking magnets does increase the field, but not always by a lot---it depends on the physical arrangement.
For your first test, make a small spacer and put two magnets one on top of the other o …
- 65.5k
16
votes
Why is it natural to make the electromagnetic field an antisymmetric, rank 2 tensor?
I think a very nice observation here is that if the force between field and current is
$$
f^a = F^{a\mu} j_\mu
$$
then in order for the force to be pure, i.e. rest-mass-preserving, it is sufficient t …
- 65.5k
0
votes
Using magnetic fields to fire plasma bolts
You can accelerate charged particles using electric fields, and you can create electric fields by various methods, including for example by a making time-varying magnetic field.
There is a lot of soph …
- 65.5k