Hertz, Heinrich Rudolf (1857 - 1894), was born in Hamburg. While at school, he showed an aptitude for sciences as well as languages, learning Arabic and Sanskrit. He studied sciences and engineering in the German cities of Dresden, Munich and Berlin. He was a student of Kirchhoff. Through experimentation, he proved that electric signals can travel through air, which is the basis for the invention of radio. He also discovered the photoelectric effect (which was later explained by Albert Einstein). In 1888, he was the first to demonstrate the existence of electromagnetic radiation by building apparatus to produce radio waves.
The SI unit of frequency, the Hertz, is named in his honour.

Hallwachs, Wilhelm (1859-1922), A German physicist, born in Darmstadt. He was professor of physics at Dresden Technical Institute. In 1888 he discovered that certain substances emit electrons when exposed to light. This is the underlying principle of the photoelectric cell. Hallwachs demonstrated the possibility of using photoelectric cells in cameras.

Philipp von Lenard was born in Austria-Hungary in 1862. He studied physics under Bunsen and Helmholtz and in 1886 took his Ph.D. at Heidelberg. Lenard's first work was done in the field of mechanics. Soon he became interested in the phenomena of phosphorescence and luminescence. Afterwards, Lenard extended the work of Hertz on the photoelectric effect. He used a good quality vacuum and showed that when ultraviolet light falls on a metal it liberates electrons. By exact measurements he showed that the number of electrons released is proportional to the energy carried by the incident light, whilst their kinetic energy, is independent of this number and varies only with the wavelength and increases when this decreases. In the course of his work Lenard invented a photoelectric cell which has many widespread applications today. He was awarded the 1905 Nobel prize for Physics.

Planck, Max Karl Ernst Ludwig (1858-1947) was born in Germany in 1858, and educated at the universities of Munich and Berlin. In 1900 Planck proposed that energy is radiated in small, discrete units, which he called quanta. By developing his theory further, he discovered a universal physical constant of nature, which came to be known as Planck's constant. Planck's law states that the energy of each quantum is proportional to the frequency of the radiation. Planck's discoveries, which were later verified by other scientists, were the basis of an entirely new field of physics, known as quantum mechanics.
Planck received the 1918 Nobel Prize for Physics. He died at Göttingen on October 4, 1947. Among his writings that have been translated into English are Introduction to Theoretical Physics (1933) and Philosophy of Physics (1936).

Maxwell, James Clerk (1831 - 1879) Scottish physicist, widely considered to be one of the greatest scientist of the 19th century. His work included the formulation of electromagnetic theory based on Faraday's observations of electric and magnetic field lines. He also calculated that the speed of propagation of an electromagnetic field is approximately that of the speed of light and concluded that light is therefore an electromagnetic wave. His work fundamentally changed the understanding of electromagnetism and introduced the basis of field theory. He also contributed to thermodynamics and the kinetic theory of gases.

Thomson, William (later Lord Kelvin) attended Glasgow University from the age of 10, where his father was chair of mathematics. When he was 16, he went to Cambridge and by the age of 24 had proposed the absolute scale of temperature that still bears his title…The Kelvin scale. Like many of his contemporaries, Thomson thought that Physics was more or less all discovered and that little remained to be done. In his words: "There is nothing new to be discovered in physics now. All that remains is more and more precise measurements”.

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Hertz

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Planck

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