# Oscillating Dipole: Principle of Receiving and Transmitting Electromagnetic wave?

I am practising to Tfy-0.1064 -elementary-physics-exam and doing this practise -exam here. The problem in Finnish goes like this:

"Selosta lyhyesti sähkömagneettisen säteilyn lähettämisen ja vastaanottamisen periaate."

and its translation is:

"Outline the principle of transmitting and receiving Electromagnetic wave."

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um... huh? It's not at all clear to me what you're asking... – David Z Sep 2 '12 at 20:08
"Specifically, if you want to study absorption and emission, you would have to study the effects of accelerating a charge and effect of light absorption on motion of charge. While if you want to study receiving and transmission, you would have to study the osciallting dipole and its equations." <-- two different questions: one is more about chemistry-physics and one is more about math-physics. chat.stackexchange.com/transcript/message/6043987#6043987 – hhh Sep 5 '12 at 22:39
@DavidZaslavsky I mis-translated the exam! Sorry I have never studied this in the exam -language...now it should be correct. Clear now? – hhh Sep 5 '12 at 22:40
Something here. – hhh Sep 6 '12 at 5:39

## 1 Answer

I don't know yet what the question is looking for, some possible scenarios.

1. Outline oscillating-dipole, the basic idea behind antennas, about transmitting and receiving

I am unable to outline this but some facts -- hopefully someone can do this!

The magnetic dipole moment is $\bar p(t)=p_0\cos(wt)\hat z$. Its maximum is when $p_0 =q_0 d$ according to the Griffiths Introduction to Electrodynamism, about p.445, covering the oscillating dipole.

2. outline the Planck-rule and cover some sub-atomic -behaviour about energy-levels.

Electromagnetic wave move in the direction of the Poytingen -vector, $\bar S=\bar E \times \bar H$. Its carried energy is related to this vector. When the wave hits a surface, the valence-shell -electrons of the surface material become more energetic. Because the amount of emitted energy is quantified, emittance will not happen unless a certain energy-level is surpassed namely determined by the Planck-rule $E=hf$. So absorbing won't happen if insufficient amount of energy is transferred from EM -wave into the valence-shell -electrons. If sufficient amount of energy is transferred from EM -wave into the valence-shell -electrons, then emittance will happen.

The Planck -rule and particularly the equation $E=\frac{hc}{\lambda}$ (more here)

Since the Planck-value $h$ is a constant, the speed of light $c$ is a constant and the wavelength $\lambda$ is a constant for an EM -wave, you need an quantified amount of energy, namely $E_k = k\left(\frac{hc}{\lambda}\right)$ -amount of energy, to ignite $k$ -amount of photons (I am not sure whether they are always photos but anyway some simplification here). When the emittance happens, the electrons will move to lower energy levels in the atoms, possibly inversely in the case of absorbance.

Evalution and some critique about the "short" outlining

I did some simplifications. If you have EM -wave consisting of different wavelengths, then the situation and the mechanisms are not probably this simple. The basic idea is however the above, things won't change that much even with different wavelengths. Let's consider $v=\lambda f$. If $\lambda$ is larger, then frequency $f$ must be smaller, meaning more energetic EM assuming the same speed.

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