Blog of Veikko M.O.T. Nyfors, Hybrid Quantum ICT consultant

Quantum Mechanics demystified, a try

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Electromagnetic radiation

Third part of electromagnetism.

Stable, steadily moving and accelerating electric charges behave differently with their associated EM fields, as decribed in electromagnetism
Accelerating charge will emit photons, i.e. it creates electromagnetic radiation.

Why is the charge accelerating?
Consider an electron on an atom’s orbital. When it absorbs a photon, it will excite to a higher energy level. Meaning it changes it’s location further away from nucleus. That necessarily involves acceleration of the electron in question. And another photon is then released in minuscule time => elctromagnetic radiation!

But where did the absorbed photon then come from?

It all starts in nuclear reactions.
Fusion reactions are taking place in stars all over our universe. Specifically in the sun, which matters the most to us on earth.
Fission reactions take place in the stars towards the end of their life cycle, in supernova phase. When all initial material required in fusion (H, He, etc) have ran out, star enters supernova phase, in which also fission reactions are occurring.
Here on earth, we cause fission reactions in our nuclear plants.

In fusion and fission gamma radiation is released.
Gamma radiation is form of electromagnetic radiation, i.e. photons. Gamma photons are the most energetic photons, having the shortest wavelength. These gamma photons then excite electrons on various types of atoms on the way (to earth ;). While these then relax, new photons are emitted with frequencies typical to the material in question. Including visible light.
In fusion also beta radiation is emitted. Beta radiation consists of free electrons. Being accelerating charges, these generate electromagnetic radiation as well.

Electromagnetic radiation can also be caused by accelerating ions.
Solar winds are flows of ions from sun’s outer layers. Nortrhern lights are born due to magnetic field changes associated with electric fields of solar winds.

When electric charges oscillate in a conducting wire, as with alternating current, fluctuating electric and magnetic fields are generated around the wire. This electromagnetic field only fluctuates around the wire, it doesn’t propagate further into the environment.
Let’s establish a condition, where the wire with AC current is not a closed circuit, but has two loose ends instead. This is easily achieved by bending the wire in T shape and putting AC generator at the bottom of T’s leg.
In the leg’s two wires electrons move to opposite directions which make the electric and magnetic fields to cancel each other out. But in T’s hat, which is a kind of rod, electrons start to accumulate in either of the loose ends, depending on the direction of the AC current at the time. We now have a rod where electrons move back and forth between the ends. Rod becomes an oscillating dipole. In this dipole, EM waves no longer only fluctuate around the rod, but they detach from the rod and propagate to the environment. A transmitting dipole antenna is born.
Same T shaped setup can be used as a receiving antenna, if we replace AC generator with a magnetic coil. When EM waves are received on the drod, electrons start to oscillate between rod’s ends, and magnetic coil at the bottom will react on the alternating current producing the desired effect, the broadcast.