Who was Hertz?
Teaching Guidance for 14-16
A very short biography of Heinrich Hertz
It's always worth bringing physics to life by introducing some of the characters behind the names. Rather than just stating that frequencies are measured in hertz, let's hear a bit about the man himself. Heinrich Hertz was born in Hamburg, Germany, on 22 February 1857. In 1880 he obtained a PhD in physics from the University of Berlin before taking up a post as a lecturer in theoretical physics at the University of Kiel in 1883.
In 1865, Maxwell's theory of electromagnetism was published and predicted the existence of electromagnetic waves moving at the speed of light, concluding that light was just such a wave. This challenged experimentalists to generate and detect electromagnetic radiation using some form of electrical apparatus.
The first clearly successful attempt was made by Hertz in 1886. For his radio wave transmitter he used a high-voltage induction coil, a condenser (capacitor, Leyden jar) and a spark gap. The sides of the gap terminated in spheres of 2 cm radius, between which there would be a spark: oscillating at a frequency determined by the values of the capacitor and the induction coil.
To prove there really was radiation emitted, it had to be detected. Hertz used a piece of copper wire, 1 millimetre thick, bent into a circle of 7.5 cm diameter, with a small brass sphere on one end, and the other end of the wire was pointed, with the point near the sphere. He added a screw mechanism so that the point could be moved very close to the sphere in a controlled fashion. This
receiver was designed so that current oscillating back and forth in the wire would have a natural period close to that of the
transmitter described above. The presence of oscillating charge in the receiver would be signalled by sparks across the (tiny) gap between the point and the sphere (typically, this gap was hundredths of a millimetre).
In more advanced experiments, Hertz measured the velocity of electromagnetic radiation and found it to be the same as that of light. He also showed that the nature of radio wave reflection and refraction was the same as that of light and established beyond any doubt that light is a form of electromagnetic radiation described by the Maxwell equations.
In recognition of his work, the unit of frequency – one cycle per second – is named the
hertz in his honour.
Heinrich Hertz died on 1 January 1894 aged 36.