Two sets of waves in a Hertzian Dipole?

AI Thread Summary
In a Hertzian dipole, the near field exhibits changing electric and magnetic fields that are in quadrature, leading to a question about the creation of two sets of electromagnetic waves in the far field. However, only one radiated wave exists, as the Poynting vector requires both electric and magnetic fields to be in phase to radiate power. Quadrature phase fields represent energy storage rather than power, as illustrated by the integral of their product being zero. The far-field radiated wave maintains a specific E:H vector ratio of 377:1, with polarization aligned along the electric field. Ultimately, changing induction fields do not contribute to radiating far fields, consistent with Maxwell's equations.
barton
Messages
14
Reaction score
1
In the near field, a hertzian pole has a changing electric field and a changing magnetic field, that are in both space and time quadrature. Are two sets of EM waves then created in the far field, one from the changing e-field, and one from the changing m-field?
 
Physics news on Phys.org
There is only one radiated wave; The radiated Poynting vector P = E x H requires both an E vector and an H vector in phase. A quadrature phase field is an induction field (like in Faraday induction, where voltage is proportional to dB/dt), and cannot radiate power. The far-field radiated wave has the E:H vector ratio of 377:1 in the mks system. The polarization is along E.
 
Last edited:
Don't the changing induction fields create the radiating far fields, as described by Maxwell's equations?
 
If two fields are in time (phase) quadrature, They represent energy storage, not power. The integral of [sin(wt) x cos(wt) dt] over 2 pi is zero. Consider the voltage and current for a pure inductance. They are in phase quadrature, and there is no real power.
 
Thread 'Question about pressure of a liquid'
I am looking at pressure in liquids and I am testing my idea. The vertical tube is 100m, the contraption is filled with water. The vertical tube is very thin(maybe 1mm^2 cross section). The area of the base is ~100m^2. Will he top half be launched in the air if suddenly it cracked?- assuming its light enough. I want to test my idea that if I had a thin long ruber tube that I lifted up, then the pressure at "red lines" will be high and that the $force = pressure * area$ would be massive...
Back
Top