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Results tagged with electromagnetism
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user 159486
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.
1
vote
A 12th-grade physics question about inductors
The electricity model which is commonly learned in schools is best described as a "lump model": We ignore all the details (contained in Maxwell's equation) and describe the result using electrical com …
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0
votes
When does the magnetic field do work?
Work is defined by force times displacement, $dW = \vec F \cdot d\vec s = F \cdot ds \; \cos(\alpha)$, where $\alpha$ is the angle between the force and the displacement. If the force and the displace …
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4
votes
Intuition for magnetic dipole moment
To understand why the area appears in the definition, we need to consider a rectangular current carrying wire with side lengths $a$ and $b$ in a magnetic field $B$
Using Lorentz's force, we know tha …
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1
vote
Accepted
Why does a magnet not move in presence of an electric field?
The magnetic moments of the electrons are the building blocks of ferromagnets:
The magnetic moment of an atom is associated with the spins of the valence electrons. If we have a single valence electro …
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2
votes
sin v/s cos-both give the same answer?
As you probably know the sin and cos functions are equivalent, as they are simply shifted by a fixed phase (=angle), $sin(wt) = cos(wt-\pi/2)$. Therefore, we can choose either function.
The key to the …
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0
votes
Producing constant constant electric field
This is covered by Maxwell's equations. One of these equations states that
the time derivative of a magnetic field generates an electric field,
$\frac{dB}{dt} \propto E
$. Hence, if we change the magn …
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0
votes
Force and potential energy between two magnetic dipoles
Why do you believe that "... the expression for 𝑈 is obtained by considering the work done in rotating the coil against the external B-field from a perpendicular starting point"? Do you have a refere …
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1
vote
Accepted
Electromagnetic waves how many polarizations for numberwaves?
We are free to choose our coordinate system. Thus, let's choose the $z$ direction to be parallel to the wave vector, $\vec k \parallel\vec z$. Since the electro-magnetic field is transverse in nature, …
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1
vote
How do the evanescent waves contribute/cause a diffraction limit?
Suppose our object is described by the function $g(x,y,z=0)$. We can write this function as a superposition of plane waves (Fourier decomposition),
$$
g_{object}(x,y,z=0) = \iint df_x df_y \;G(f_x, f_ …
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3
votes
What happens, electromagneticaly, when you push something?
No, it's not the electro-magnetic force, which is responsible for the interaction between the two bodies. Instead, it's the so called Pauli's principle (or Pauli's exclusion principle), which in fact …
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1
vote
Waves interference in terms of fields and intensity
If we consider the interference pattern on a ccd camera due to the superposition of two coherent waves, both descriptions are equivalent. To see this, let's start with two $sin$-waves, as you did. To …
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1
vote
Why can't the current in a solenoid be changed rapidly?
I'm not sure about your background -- which physics level you got. So I will only use "school" arguments to explain the effect.
The key characteristic of a coil with a running current is that it is an …
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1
vote
Huygens' Principle alternative explanation on reflection
The picture is rather small, but I can see small parts of circles. If you would blow it up, we obtain the following
The incident wave travels perpendicular to $\overline{A_1B_1}$.
At time $t_2$ the …
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2
votes
Could a magnetic field with a direction opposite the Earth's be repelled?
The situation is best described by two magnetic dipoles. Since opposite magnetic pols attract each another and the same magnetic poles repel each other, one could in principle obtain a mere repulsive …
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0
votes
How to approximate electromagnet-magnet interaction
If you are interested in the static problem, you could use the following steps:
Use Biot-Savart's law to calculate the magnetic field $\vec B(x,y,z)$. Use a grid to obtain the field at different posi …
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