# Tag Info

## Hot answers tagged electromagnetism

39

Photonics is a thing, and it very much treats light as electromagnetic waves in waveguides on silicon, with mixers, delay lines, matching circuits, amplifiers etc as you'd do for a RFIC. Just as an antenna doesn't generate the signal to be transmitted, an oscillator is used to generate a carrier wave – just that the oscillator happens to be a laser diode, ...

17

The wavelength of 750 THz is 400 nm so, your dipole would need to be 200 nm long to make a radiating antenna but your biggest problem (in 2021 and probably beyond) is being able to produce a frequency of 750 THz. Leave it to the optical guys is my advice. Another consideration (from classical Friis equations) is that the path loss (from a transmitting ...

10

The other answers are correct, the frequency of light (i.e., visible light) is so fast that it's really hard to do. People do make THz light (even longer wavelength than infrared) using antennas, and can even make mid-infrared light using nanometer scale antennas - but this is highly technical, requires teams of scientists, and millions of dollars. There is ...

8

Here is an open access paper describing an Yagi-Uda antenna emitting light at 830 nm. Kullock, R., Ochs, M., Grimm, P. et al. Electrically-driven Yagi-Uda antennas for light. Nat Commun 11, 115 (2020). https://doi.org/10.1038/s41467-019-14011-6

5

An electromagnetic field is created when a current passes through a wire This is entirely correct. As far as I know, since the current is DC, there is a magnetic field (since current is moving), but there is no electric field It is true in a certain sense, and under certain conditions, that a DC current through a wire creates a magnetic component of a ...

4

No, it isn't possible. The properties of the materials are very different at such frequencies. Consider the materials typically used in chip manufacturing. We use aluminum as a conductor, and silicon dioxide (glass) as an insulator. But at 750 THz, aluminum blocks the EM field, either reflecting it or absorbing it as random thermal energy. And glass passes ...

3

It depends on the conduit if it is a conductor or not. In fact the heat due to magnetic field is not from the cable but on the conduit and it is produced by the eddy currents induced by the magnetic field in the metallic conduits. That is why in case of metallic conduits cables are arranged in order to cancel the magnetic field. It is true also for three-...

3

OP @clone is correct in saying the diagrams do not represent a generator. Curling the fingers of the right hand around the wire, with the thumb pointing in the direction of current flow assuming a generator results in the contradiction of the magnetic field being reinforced on the leading side of the rotor, not the trailing side. The contradiction means the ...

2

The first danger to consider is the danger of dielectric breakdown, and consequent current through the body between the plates. If however, that danger were somehow eliminated, the next danger I would consider applies to an alternating electric field. Depending upon frequency and amplitude, a body between two conductive plates with an alternative electric ...

2

That website (at the top of the page) shows a picture of 3 cute kids playing with test-tubes, pencils and a microscope. That to me gives a strong clue as to whom the page's target audience is. The field created by a DC current passing through a coil is magnetic. You could argue that there is an electric field created by the initial transient of applying a ...

2

two adjacent wires forward and return will have lower inductance as the mutual coupling reduce EMI and loop inductance somewhat But this only increases apparent power a tiny bit at 1uH/m per wire and has no effect on real power. Putting two lossy distribution lines in the same thermal resistive jacket inside a conduit ought to increase heat rise. yes a ...

1

Per KD9PDP above, about 40 years ago I encountered another ham with a VERY strong signal on 75 meters single side band. It turns out he was running 3kW peak IN HIS CAR! To accomplish this, he had a specially wound 3 phase generator under the hood that generated high voltage and reduced the complexity of his linear amp power supply. When he spoke, a ...

1

what is the behaviour of a flywheel/dynamo system in relation to the electrical load being served? Assuming 100% power efficiency in the dynamo, whatever electrical power is being removed from the dynamo to drive an electrical load is seen as a mechanical power burden on the flywheel and that of course will gradually slow down the flywheel. That mechanical ...

1

In other words, is the electric field between the plates the original external incident E field or is it the E field generated by the charges separated by the original incident E field? Using Superposition theorem Electric field between the plates is due to 1.Electric field of electromagnetic wave 2.induce charges of 1st plate 3.induce charges of 2nd plate ....

1

Well, if your system is described by $$m\frac{d^2H}{dt^2} = mg-K\frac{I^2}{H^2}.$$ With the state $$x := \begin{bmatrix}H \\ \dot{H}\end{bmatrix}$$ we have that $$\dot{x} = \begin{bmatrix}\dot{H} \\ g-K\frac{I^2}{mH^2}\end{bmatrix}.$$ For any $h>0$ the point $x_{eq} = \begin{bmatrix} h \\ 0\end{bmatrix}$ will be an equillibrium, since \\$\forall h&...

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