All Questions
55
questions
14
votes
4
answers
5k
views
Why are EM plane waves transverse?
I was reading Griffiths' Introduction to Electrodynamics, specifically Section 9.2.2 on plane waves. I can see that if we want a transverse wave traveling in the $z$ direction that we are only going ...
- 561
5
votes
1
answer
545
views
Why do planets not radiate EM waves in their orbits?
Despite being overall near-netural, I would expect the individual electrons and proton to radiate long EM waves as we accelerate around the Sun or rotate around our poles. Is the acceleration so small ...
- 163
5
votes
2
answers
4k
views
Make a semi transparent mirror with copper
The question:
How would you make a semi transparent mirror (50% reflection, 50% transmission) with glass with a layer of copper. For light $\lambda$ = 500nm Try to be as realistic as possible
What I'...
- 215
5
votes
2
answers
5k
views
Force on Earth due to Sun's radiation pressure
I have been asked by my Classical Electrodynamics professor to calculate the force that the Sun exerts in the Earth's surface due to its radiation pressure supposing that all radiation is absorbed and ...
- 727
3
votes
3
answers
621
views
Tricky question involving finding the magnetic field given the wave equation for the electric field and it's solution
Consider the wave equation for linearly $x$ polarized waves travelling in the $\pm z$ directions:
$$\frac{\partial^2\vec E_x}{\partial t^2}=c^2\frac{\partial^2\vec E_x}{\partial z^2}\tag{1}$$
...
- 2,470
3
votes
2
answers
2k
views
Proof that $||\vec{E}|| = c||\vec{B}||$ for electromagnetic waves from maxwells equations in vacuum
Starting from Maxwell-equations in vacuum :
$$
\nabla \cdot \vec{E} = 0
$$
$$
\nabla \times \vec{E} = - \frac{\partial \vec{B}}{\partial t}
$$
$$
\nabla \cdot \vec{B} = 0
$$
$$
\nabla \times \vec{B} =...
- 297
2
votes
1
answer
1k
views
Confusion even over such a simple application of the Right-hand rule to determine direction of magnetic field
After reading this question on this site I learned that the direction of the magnetic field is given by $\boldsymbol{B}=\frac{1}{\omega}\boldsymbol{k}\times \boldsymbol{E}$
The left diagram below is a ...
- 295
2
votes
3
answers
5k
views
A charged sphere with pulsing radius
Radius increases and decreases periodically (as a pulse).And so does the charges on the surface of sphere.
I can't get what is gonna happen.the EM waves are produced perpendicularly to motion of the ...
- 2,479
1
vote
3
answers
13k
views
Deriving the wave equation for electromagnetic waves
I'm currently referring to the wave equation derivation given in "Introduction to Electrodynamics" by David J. Griffiths. It follows something like this:
The electromagnetic wave equations are given ...
- 87
1
vote
4
answers
3k
views
Can a wave's Poynting vector be in the opposite direction compared to its direction of propagation?
Can a wave's Poynting vector be in the opposite direction compared to its direction of propagation, and if so, what physical implications does it have?
As I understand, the poynting vector s can be ...
- 11
1
vote
1
answer
248
views
Derive the form of the fields for TEM waves in a waveguide
In my book it says that for TEM waves in a waveguide, with: $$\textbf E = \textbf E_0(x,y)e^{i(kz-\omega t)}$$ and $$\textbf H = \textbf H_0(x,y)e^{i(kz-\omega t)},$$ where $z$ is the direction of the ...
- 789
1
vote
1
answer
861
views
Electric field of uniformly moving charge ; misprint in Feynman textbook? (28.3)
I doubt about formula (28.3) from this Feynman's lecture.
$$\textbf{E} = - \frac{q}{4 \pi \epsilon_0 } \Big{[} \ \frac{e_{r'}}{r'^2}+ \frac{r'}{c} \frac{d}{dt} \Big( \frac{e_{r'}}{r'^2} \Big) + \...
- 115
1
vote
1
answer
294
views
How do integral representations of $\mathbf A$ and $\Phi$ satisfy Lorenz condition?
The following are the integral solutions of the potentials, obtained from the retarded potentials (by a Fourier transform):
$$\mathbf A (\mathbf r) = \frac{\mu_0}{4\pi}\int_V \frac{\mathbf J (\mathbf ...
- 903
1
vote
1
answer
31
views
Effect of incident angle on wavelength of transmitted wave for normal polarisation?
In my electrodynamcis assignment I'm being asked to derive the wavelength of a normally polarised wave transmitted through a glass/air interface as a function of $n_1$ (the refractive index of the ...
- 11
1
vote
1
answer
3k
views
EM-Wave: Calculate magnetic field $H$ from electric field $E$
In an exercise I am supposed to calculate the magnetic field from the electric field for a plane, harmonic wave in vacuum.
$$\vec{E} = - E_0 \cdot \sin(\omega t - k z) \cdot \vec{e_y}$$
Using the law ...
- 247