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Results tagged with electromagnetism
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user 31895
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 we say induced emf depends on the path considered?
can I say that we can associate value to induced emf between any two points over some arbitrary path?
Yes.
Can we conclude induced emf over any imagined path does not depend on whether there is som …
- 41.2k
1
vote
Does $\vec F=I\int\mathrm d\vec{l}\times \vec{B}$ give the force on a current carrying wire ...
You are correct; although the usual simple derivation works only for stationary conductor, the result is more general and holds for moving conductor as well.
One way to see it is the argument you gave …
- 41.2k
1
vote
Are we always allowed to treat an inductor as a battery with the same voltage?
Your equation
$$
V_{bat} -V_{inductor} = RI,~~~\tag{inconsistent signs}
$$
has inconsistent signs in front of $V$'s, which makes the equation true only if inconsistent definitions of signs of $V$'s ar …
- 41.2k
1
vote
Accepted
Deriving Faraday's law from a special case, do we consider Lorentz force on electrons only o...
Motional emf in a circuit, which is EMF due to motion of the circuit in magnetic field, is defined as
$$
\mathscr{E}_{motional} = \oint_{circuit} d\mathbf s \cdot (\mathbf v \times \mathbf B_{ext}),
$ …
- 41.2k
2
votes
How to get the formula of the energy of EM waves?
Is it possible to derive the quadratic energy expression from the wave equation and Lorentz force?
This is not possible, because those equations do not involve EM energy. EM energy has to be defined …
- 41.2k
5
votes
Accepted
Incorrect proof that four-current $J^\mu$ is a four-vector
Let's start with an even simpler example. Let there be a single-component function of coordinates $\phi$, which obeys the equation
$$
\partial_\mu \phi = 0
$$
in all frames. Does this imply value of $ …
- 41.2k
1
vote
What makes classical Rutherford model unstable?
The atom in the planetary Rutherford model is stable, because the electron is moving in a central Coulomb field of nucleus, and for such field, stable orbits are possible, just like for motion of a ma …
- 41.2k
1
vote
Using KVL in a changing magnetic field
This is a frequent question and often people are quite confused about it. The way to clear up confusion and answer the question starts with realizing what voltage in the KVL means.
The voltages referr …
- 41.2k
2
votes
Accepted
Are the accelerated charges the real reason for the magnetic induction?
Yes, this explanation works in cases where the EMF is due to electric current in a stationary circuit changing in time. Magnetic flux is proportional to current, so according to the Faraday law, induc …
- 41.2k
0
votes
Why doesn't an EMF source directly affect the internal charges in a wire, but only the surfa...
does the battery field only affect surface charges, or both surface and inner charges.
In stationary regime, inside a uniform conductor, whether the current is zero or not, net charge density vanish …
- 41.2k
2
votes
Is there an electric field due to current carrying wire?
If the current flows in a conductor with non-zero resistance, then there is non-zero electric field inside, because without it current wouldn't flow constantly. This electric field can only come from …
- 41.2k
3
votes
Accepted
Lorentz force on objects
but the magnetic field does no work since when we take the work integral , due to cross-product and v being parallel to ds, the dot product becomes 0.
In macroscopic EM theory, magnetic force on a m …
- 41.2k
0
votes
Doubt when considering the signs for the Lagrangian for a charged particle in an electromagn...
The preferred formula to teach, for the Lagrangian of non-relativistic charged particle in external field, is
$$
L(\mathbf r,\mathbf v,t) = \frac{1}{2}mv^2 - q\phi(\mathbf{r},t) + q\mathbf{v}\cdot \ma …
- 41.2k
0
votes
Why is there an electric field but not magnetic field on the LHS of the integral form of Far...
He considers only EMF due to induced electric field. The emf depending on external magnetic field you find missing is called motional emf, and can be present only when a part of the circuit is moving. …
- 41.2k
2
votes
Why is radiation power defined at infinity?
This is one of the places where Griffiths is less conceptually correct and clear than elsewhere in the book.
Griffiths, in that section, is saying what a litmus test for radiation is, but his test act …
- 41.2k