Philipp Lenard

Written by Vanshika Balayan

Living from June 7th, 1862 to May 20th, 1879, Philipp Eduard Anton von Lenard was a German scientist who studied the physics behind cathode rays.[2]

Personal Life

Lenard was a nationalist and a known ant-Semite. He was an active proponent of Nazi ideology and was an important role model for the "Deutsche Physik" movement

Life and Education

Philip was born in Bratislava (Hungary), on 7 June, 1862. His family originated from Tyrol and were German speakers. Philipp von Lenardis, his farther, was a wine merchant in Pressburg and his mother's name was Antonie Baumann. Philipp attended the 'A Pozsonyi királyi katholikus fögymnasium´, which really had a big effect on him and made him want to pursue the sciences during his tertiary education. He then studied physics and chemistry in Vienna and Budapest in 1880. After receiving his doctorate and working under different scientists for a good bit of time, he moved to the University of Heidelberg in 1907 as the head of the Philipp Lenard Institute. The year 1905 brought him membership to the Royal Swedish Academy of Sciences and 1907 brought him membership at the Hungarian Academy of Sciences. [3]

Work

Photoelectric Findings

In 1888, Lenard began his study of cathode rays, which is where he made his biggest contributions. Lenard devised a method that made small metallic windows in the glass tubes that had allowed him to pass the rays emitted from the cathode into the laboratory or into an evacuated chamber. These windows were named "Lenard windows". The creation of these windows then helped him observe the absorption of the rays. He saw that the absorption of the rays was proportional to the density of the material they were made to pass through. This contradicted the previous notional that cathode rays were some type of electromagnetic radiation. Additionally, Lenard saw that the rays appeared to be scattered by air after a short period of time, thus implying that cathode rays were negatively charged energetic particles. He called these quanta. This helped all physicists realize that electrons are constituent parts of an atom and that atoms mostly consist of empty space.

Lenard's most important observation was that the energy of a cathode ray is independent of the light intensity, but was greater for shorter wavelengths of light. These observations were then further explained by Albert Einstein in what he called the quantum effect. This theory showed that the energy of a cathode ray should be directly proportional to frequency by a factor of Planck's constant, h.

Lenard actually ended up being a skeptic of Einstein's theories. However, he never went against Einstein's explanation of the photoelectric effect.

ElectroMagnetism

In the 19th century, the connection between electricity and magnets was studied fervently by European scientists after the work of Hans Christian Oersted, Jean-Baptiste Biot and Félix Savart highlighted this connection. All of these scientists provided support for Maxwell's work, but Michael Faraday provided the most inspiration for Maxwell in his studies. However, Maxwell differed from Faraday in that he looked at the mathematical aspect of his research in addition to the physical aspects.

Maxwell's first step towards his electromagnetic theory was in his paper On Faraday's lines of force (1864), in which he proposed the idea of an incompressible fluid, the flow lines of which could represent the electric or magnetic field or current flow [4]. Here he explained that, in the case of electric fields, sources of the flow lines were positive charges and sinks were negative charges. In his subsequent paper, Maxwell introduced the idea of vortices, small, elastic objects that occupy space and have a small mass. Using this idea, he was able to derive Ampère's circuital law and to provide an explanation of Faraday's law of induction. In his model, these vortices were able to move in a conductor, but not in a dielectric (insulator). However, in a dielectric, the vortices can shift slightly due to an electric field.

Equations

In a paper titled A dynamical theory of the electromagnetic field, Maxwell strove to make his theories more mathematical and less analogical. His four equations that resulted from this are as follows.

1. Gauss' law for electricity: [math]\displaystyle{ \oint \overrightarrow{E} \bullet d \overrightarrow{A} = \frac{q} {\epsilon_0} }[/math]

2. Gauss' law for magnetism: [math]\displaystyle{ \oint \overrightarrow{B} \bullet d \overrightarrow{A} = 0 }[/math]

3. Faraday's law of induction: [math]\displaystyle{ \oint \overrightarrow{E} \bullet \overrightarrow{d s} = -\frac{d \Phi} {dt} }[/math]

4. Ampere's law: [math]\displaystyle{ \oint \overrightarrow{B} \bullet \overrightarrow{d s} = \mu_0i + \frac{1} {c^2} \frac{\partial} {\partial t} \int \overrightarrow{E} \bullet d \overrightarrow{A} }[/math]

Use by Other Scientists

Albert Einstein once said "The special theory of relativity owes its origins to Maxwell's equations of the electromagnetic field."[5] Einstein was said to have a picture of Maxwell on his wall in his study. [6]