Description of the intangible – wave or particle

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The electromagnetic radiation spreads out in space in the form of waves. They consist of an electric and a magnetic field, which are perpendicular to each other and pulsate in a spatially arbitrary, but always perpendicular to the direction of propagation, plane. The best way to imagine this is in the form of a standing and a lying sine wave. We call this type of wave transverse because its oscillating part is lateral, or perpendicular, to the direction of propagation. Electromagnetic waves propagate at the speed of light (299,792.458 km per second) and, in contrast to sound waves, do not need a carrier and can therefore propagate in a vacuum. Their characteristics are the wavelength, the distance between two successive wave crests, the amplitude, the vertical distance between wave crest and trough, and the frequency, which indicates the number of oscillations per time unit. Many different radiating bodies surround us, permanently engulfing us in a wide range of electromagnetic radiation across the most diverse wavelengths and frequencies.

We will conduct an experiment together to understand the creation of long-wave electromagnetic radiation, or radio waves. Heinrich Hertz, who named the unit of frequency, conducted this experiment at the end of the 19th century. Hertz created electrical oscillations by applying an electrical charge to one end of a metal rod (dipole), which was about 30 cm long and a few millimeters thick, for a brief period using a spark discharge method. This generates a voltage between the two ends of the rod, thereby creating an electric field that stores the energy. Current flow balances this voltage between the two ends of the rod, creating an electric field that in turn stores the energy. When the current flow is at its maximum, the magnetic field also reaches its maximum value. If the current flow decreases, the magnetic field also decreases, and induction ensures that the current persists in the rod in the opposite direction. The dipole repeats this process of periodic energy conversion between the electric and magnetic fields in the opposite direction, generating the electric oscillation we graphically understand as an electromagnetic wave. Since the wavelength of the electromagnetic radiation is twice as large as the dipole itself, such a dipole is well suited to generate waves in the range of centimeters or meters. Wavelengths below one centimeter, on the other hand, are difficult to generate in dipoles. In this range, conductive cavities are usually used as oscillators. Molecules or atoms then reserve even shorter wavelengths. Even though an atom with a diameter of approximately 0.1 nm is significantly smaller than the average wavelength of visible light at 500 nm, we still observe the previously described oscillating dipole process in this context.

To understand the generation of electromagnetic radiation at the atomic level, we need to take a quick look inside any atom. There the electrons (the negatively charged particles) move radiation-free (without loss of energy) on fixed orbits around the protons (the positively charged particles) in the nucleus. The greater the distance of the orbits from the nucleus, the greater the energy level of the electron. An electron releases energy in the form of a photon each time it transitions from a higher energy level to a lower one. Conversely, the atom absorbs external energy to propel the electron in the opposite direction. Both movements are called electron jump or quantum leap and they always take place under release or absorption of the corresponding energy difference so that the energy level of the total system remains the same.

These emission and absorption processes within atoms continue to challenge physicists today, as the conventional understanding of electromagnetic radiation as a continuous wave is insufficient to fully comprehend them. Max Planck’s quantum hypothesis, which dates back to 1900, explains that an electrically oscillating system does not continuously transfer or absorb energy from an electromagnetic field, but rather does so in very small amounts, known as quanta. In 1905, Albert Einstein introduced these energy quanta into physics by explaining the photo effect, which he defined as the light particles or photons that Isaac Newton had previously propagated in the 1670s through his emission theory.

With this theoretical equipment, we can describe the light as an electromagnetic wave on the one hand and as a particle stream (photons) on the other, and only the arrangement of the respective experiment decides whether it appears in the one or the other form.

Next With the grain or against it – the polarization of electromagnetic waves

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