Heinrich Hertz

Summary

Heinrich Rudolf Hertz (22 February 1857, Hamburg – 1 January 1894, Bonn) was a German physicist.He graduated from the University of Berlin, where his teachers were Hermann von Helmholtz and Gustav Kirchhoff. From 1885 to 1889 he was professor of physics at the University of Karlsruhe. From 1889 he was professor of physics at the University of Bonn.

The main achievement was the experimental confirmation of James Maxwell”s electromagnetic theory of light. Hertz proved the existence of electromagnetic waves. He studied in detail the reflection, interference, diffraction and polarization of electromagnetic waves, proved that their speed of propagation coincides with the speed of light, and that light is a type of electromagnetic waves. He constructed the electrodynamics of moving bodies on the hypothesis that the ether is entrained by moving bodies. However, his theory of electrodynamics was not confirmed by experiments and later gave way to the electron theory of Hendrik Lorentz. The results obtained by Hertz were the basis for the creation of radio.

In 1886-1887 Hertz first observed and described the external photoelectric effect. Hertz developed the theory of resonant circuit, studied the properties of cathode rays, and investigated the influence of ultraviolet rays on electric discharge. In a number of works on mechanics he gave the theory of elastic ball impact and calculated the time of impact. In the book “Principles of Mechanics” (1894) he derived general theorems of mechanics and its mathematical apparatus from a single principle (Hertz principle).

Since 1933, the unit of frequency Hertz is named after Hertz, which is part of the International System of Units (SI).

Heinrich Rudolf Hertz was born in Hamburg on February 22, 1857. His father, lawyer and in 1887-1904 Senator Gustav Ferdinand Hertz (1827-1914), was born as David Gustav Hertz into a very wealthy Jewish family, he was a prosperous merchant and member of the Hamburg city council from 1860-1862; his mother (Heinrich Rudolf”s grandmother), Betty Augusta Oppenheim (1802-1872) was the daughter of the important banker Solomon Oppenheim, founder of the presently active Sal. Oppenheim. Both Heinrich Hertz”s grandfather and father converted to Lutheranism.

Heinrich Hertz”s mother, born Anna Elisabeth Pfefferkorn (1835-1910), was the daughter of Johannes Pfefferkorn (1793-1850), an army doctor from Frankfurt am Main, and Susanna Gadroiter (1797-1872). Heinrich had three younger brothers and a sister.

During his studies at the University Gymnasium in Hamburg, Heinrich Hertz showed an aptitude for the sciences as well as languages, learning Arabic and Sanskrit. He studied science and technology in Dresden, Munich and Berlin, where he was a student of Kirchhoff and Helmholtz. In 1880, Hertz received his Ph.D. from the University of Berlin, and remained for postdoctoral studies under Helmholtz. In 1883 he took a position as lecturer in theoretical physics at Kiel University, and in 1885 Hertz became a full professor at the University of Karlsruhe, where he made his scientific discovery about the existence of electromagnetic waves. Hertz”s work played a huge role in the development of science and technology, contributing to the appearance of the wireless telegraph, radio communications, radiolocation, and television.

Hertz always had a deep interest in meteorology, probably acquired through his contacts with Wilhelm von Betzold (he was Hertz”s laboratory professor at the Munich Polytechnic in the summer of 1878). Hertz, however, made little contribution to the field, except for some early papers as Helmholtz”s assistant in Berlin. These included a study of the evaporation of liquids, the development of a new kind of hygrometer, and the development of graphical tools for determining the properties of moist air subjected to adiabatic changes.

In 1881-1882, Hertz published two papers on what later became known as contact interaction mechanics. Although Hertz is primarily known for his contribution to electrodynamics, these two articles did not go unnoticed either. They have been the source of important ideas, and most papers that examine the fundamental nature of contact refer to them. Joseph Boussinesq made some important criticisms of Hertz”s work, while recognizing their great importance.

In these works, Hertz considers the load behavior of two axisymmetric objects in contact. The results obtained are based on classical elasticity theory and continuum mechanics. The most significant shortcoming of his theory was the neglect of adhesion of any nature between two solid bodies, which turns out to be important when these bodies begin to behave elastically. At that time, it was quite natural to neglect it, since there were no experimental methods for its investigation at that time.

To substantiate his theory, Hertz investigated the behavior of elliptical Newton rings formed by placing a glass sphere on a lens. He believed that the pressure exerted by the sphere on the lens would cause the Newton rings to change. He used Newton”s rings again when he tested his theory in experiments to calculate the shear that the sphere causes in the lens.

From 1885 to 1889 Hertz worked as a professor of physics at the Technical University in Karlsruhe. It was during these years that he carried out his famous experiments on the propagation of electric force, which proved the reality of electromagnetic waves. The apparatus used by Hertz may seem more than simple now, but his results are all the more remarkable. His sources of electromagnetic radiation were sparks in the arrester. The electromagnetic waves from the arresters caused spark discharges between the balls in “receivers” – circuits located several meters away and tuned to resonance. Hertz managed not only to detect waves, including standing waves, but also to study their speed of propagation, reflection, refraction, and even polarization. All this was very similar to optics, with the only (very significant!) difference being that the wavelengths were almost a million times longer (about 3 meters).

Hertz radio transmitter based on the Rumkorff coil (with shock excitation of the oscillating circuit by a key breaker). Direct current from the source, passing through the coil, magnetizes its iron core, it attracts a movable contact and the circuit breaks, when the magnetic field disappears the contact closes again.To conduct experiments Hertz invented and designed his famous transmitter of electromagnetic waves, later called “Hertz vibrator”. The vibrator consisted of two copper rods with brass balls and one large zinc sphere or square plate each, acting as a capacitor. A gap was left between the balls – a spark gap. To the copper rods were attached the ends of the secondary winding of the Rumkorff coil – a low-voltage direct current to high-voltage alternating current converter. During AC pulses, sparks flashed between the spheres and electromagnetic waves were emitted into the surrounding space. By moving the spheres or plates along the rods, the inductance and capacitance of the circuit, which determines the wavelength, were regulated.

Hertz”s radio receiver (spark radio)To pick up the radiated waves, Hertz invented a simple resonator – a wire unclosed ring or a rectangular unclosed frame with the same brass balls at the ends as in the “transmitter” and an adjustable spark gap. As a result of his experiments Hertz discovered that if high-frequency oscillations occur in the generator (a spark flashes in its discharge gap), then in the discharge gap of the resonator, which is even 3 m away from the generator, small sparks will also flicker. Thus, the spark in the second circuit occurred without any direct contact with the first circuit. After conducting numerous experiments with different mutual positions of the generator and the receiver, Hertz comes to the conclusion about the existence of electromagnetic waves propagating with a finite speed. Will they behave like light? Hertz conducts a thorough test of this assumption. After studying the laws of reflection and refraction, after establishing polarization and measuring the speed of electromagnetic waves, he proved their complete analogy with light waves. All this was outlined in the work “On the rays of electric force”, published in December 1888. This year is considered the year of the discovery of electromagnetic waves and the experimental confirmation of Maxwell”s theory.

Through his experiments, Hertz came to the following conclusions:

In 1887, upon completion of the experiments, Hertz published his first article “On very fast electric vibrations,” and in 1888 – an even more fundamental work “On electrodynamic waves in the air and their reflection.

Hertz believed that his discoveries were no more practical than Maxwell”s: “It is absolutely useless. It is only an experiment that proves that Maestro Maxwell was right. We just have mysterious electromagnetic waves that we can”t see with our eyes, but they are there.” “So what”s next?” – one of the students asked him. Hertz shrugged; he was a humble man, without pretensions or ambition: “I guess nothing.

But even at the theoretical level, Hertz”s achievements were immediately marked by scientists as the beginning of a new “electric era.

To better see the spark in his experiments, Hertz placed the receiver in a darkened box. He noticed that in the box the length of the spark in the receiver became shorter. Then Hertz began to experiment in this direction, in particular, he investigated the dependence of the spark length in the case when a screen of different materials is placed between the transmitter and the receiver. Hertz found that electromagnetic waves passed through some kinds of materials and were reflected by others, which led to the appearance of radars in the future. In addition, Hertz noticed that a charged capacitor loses its charge faster when its plates are illuminated by ultraviolet radiation. These results were the discovery of a new phenomenon in physics, called the photoelectric effect. The theoretical basis of this phenomenon was later given by Albert Einstein, who received the Nobel Prize in 1921.

In 1892 Hertz was diagnosed with an infection (after a severe migraine). He was operated on several times to cure the disease, but to no avail. He died in 1894 of Wegener”s granulomatosis at the age of 36 in Bonn. He is buried in Hamburg in the Olsdorf Cemetery.

His widow Elisabeth Hertz (nee Elisabeth Doll) never married again. Hertz left behind two daughters, Johanna and Matilda. All three emigrated to England in the 1930s, after Hitler came to power. In the 1960s, Charles Suskind interviewed Matilda, which he then published in a book about Heinrich Hertz. According to Suskind”s book, Hertz”s daughters were not married, so he had no descendants. Mathilde Carmen Hertz (1891-1975), only three years old when her father died, became a famous psychologist.

Although Hertz was a Lutheran and hardly considered himself a Jew, his portrait was removed by the Nazis from its place of honor in Hamburg”s city hall because he was “part Jewish.

H. Hertz”s nephew Gustav Ludwig Hertz (1887-1975) became a famous physicist and Nobel Prize winner, while the latter”s son, Carl Helmut Hertz (1920-1990), created medical sonography.

On May 7, 1895, the inventor of radio, Alexander Popov, used an apparatus of his own invention to transmit the words “Heinrich Hertz,” which are the first words ever transmitted by radio.

In 1930, the International Electrotechnical Commission in honor of Hertz established a new unit of measurement, Hertz (Hz), used as a measure of the number of repeating events per unit time (also called “number of cycles per second”). It was adopted by the XI General Conference on Weights and Measures in 1960 as the unit of frequency in the SI system.

In 1969 a commemorative medal in honor of Heinrich Hertz was issued in East Germany. In 1987, the IEEE established the Heinrich Hertz Medal “for outstanding achievements in the study of Hertz waves,” awarded annually to theoretical and experimental scientists.

A crater on the east side of the back side of the moon is named after Hertz. The city”s broadcasting and communications tower in Hamburg is named after the famous Hamburg native.

In 1889 the Italian Society of Sciences in Naples awarded him the Matteucci Medal, the Paris Academy of Sciences the Lakaz Prize, and the Vienna Imperial Academy the Baumgartner Prize. A year later the Royal Society of London awarded Hertz the Rumford Medal, and in 1891 the Royal Academy in Turin awarded him the Bress Prize. The Prussian government awards him the Order of the Crown. In addition, Hertz was awarded the Japanese Order of the Sacred Treasure.

Sources

  1. Герц, Генрих Рудольф
  2. Heinrich Hertz
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