Recent content by terahertz

The textbook I had in mind is "Introduction to Electrodynamics", by David J. Griffiths, 4th edition, PHI . More specifically, Example 7.9, Problem 7.16, and Problem 7.36.

Yes, I am trying to calculate the rate of change of the electric field (displacement current) rather than the surface currents on the walls (conduction current).

To calculate the displacement current in a coaxial cable (with equal and opposite currents on the inner and outer conductors), most standard texts use the magnetoquasistatic approximation, which ignores the time-varying electric field term in Ampere’s Law. Using this approximation, the...

What circuit design is used to ensure that the renewable energy source does not begin to absorb energy from the grid (for instance, when its terminal voltage drops below the distribution line voltage)?

Thanks a lot for your enlightening response. Your simple example clarified a lot of things!

When you look at the emission/absorption spectrum of a single element, you can clearly see various emission/absorption lines, which are characteristic of that element. However, radiation from stars/galaxies contains spectra of many elements. How do astronomers make sense of this jumbled-up...

Thanks for your replies, UltrafastPED and ZapperZ. Let me pose my question slightly differently. The wave equation in electromagnetics is derived directly from Maxwell's equations. Therefore, if diffraction of EM waves is explained on the basis of the wave equation, then it should also be...

Sorry, typo in the title. I meant, why do they diffract in the same way.

Mechanical waves (sound, water waves) and EM waves both undergo diffraction. But the actual physical processes involved in the two are totally different. EM waves are produced by accelerated charges while mechanical waves are tiny displacements of molecules of the medium in which the wave is...

I think what was meant was that at the power-line frequency, a 1,100 km long transmission line is about one quarter wavelength long. If this length of line is terminated in an open circuit, its input impedance is zero.

AlephZero, the difference between transmission line theory and circuit theory is that the former takes into account the difference in the phase of the signal as a function of the distance along the line whereas the latter ignores it and considers the phase to constant along the line.

stevendaryl, thanks a lot! Your illustrated explanation is very clear. Now I have to see how it is equivalent to arildno's rotating disks analogy. the_wolfman, are you saying that the rotating disks analogy is over-simplistic and/or imperfect? If so, can you give another analogy? Thanks!

Thanks a lot, arildno! Actually, I know what curl and divergence mean in terms of the physical operations that we do to the vector field to get them. I have the picture of rotating disks in my mind when I think of the curl of a vector field, and of the field strengthening or weakening locally...

At the power-line frequency (50Hz), the wavelength of electromagnetic waves in free space is 6,000 km. Similarly, the phase velocity of voltage/current waves is about 4,000 km at this frequency. The question is, why do we bother about the wavelength at all at the power-line frequency, when the...

Can anyone give me an intuitive/physical reason for why the divergence of the curl of a vector field is always zero? I know various methods to prove mathematically that it is so, but have not managed to find a physical reason. In other words, why is the curl of a vector field always incompressible.