Franz Ernst Neumann

Physicist and mineralogist — Franz Ernst Neumann (1798–1895) was a German physicist and mineralogist, for most of his life a professor at the University of Königsberg. A teenage combatant at Waterloo, he went on to study mineralogy and crystallography before turning to mathematical physics. In 1845–1847 he formulated in rigorous mathematical form the law of electromagnetic induction, expressing the induced electromotive force as the derivative of the linked magnetic flux and introducing the concept of the mutual inductance coefficient. He made fundamental contributions to crystal physics with the celebrated “Neumann principle”, according to which the physical properties of a crystal possess at least the symmetry of its lattice, as well as to optics and heat theory (the Neumann–Kopp law on specific heats). Together with the mathematician Carl Gustav Jacob Jacobi, he founded in Königsberg the first seminar in mathematical physics, training a generation of German theoretical physicists and helping to make Germany the cradle of theoretical physics.

Curiosity

With Jacobi he created the celebrated mathematical-physical seminar in Königsberg, regarded as the model from which modern theoretical physics emerged as an academic discipline.

Theories and contributions

• Law of induction (Neumann’s form) — The induced e.m.f. equals the negative of the time derivative of the linked magnetic flux: $\varepsilon = -\dfrac{d\Phi_B}{dt}$.
• Mutual induction — Introduces the mutual inductance coefficient via Neumann’s formula: $M=\dfrac{\mu_0}{4\pi}\oint\!\oint \dfrac{d\vec l\cdot d\vec l'}{r}$.
• Neumann principle — The physical properties of a crystal have at least the symmetry of the crystal’s point group.
• Neumann–Kopp law — The molar specific heat of a solid compound is approximately the sum of the specific heats of its constituent elements.

Present in chapters

18 19 Z

Linked atoms

14 linked atoms.

18 Induzione elettromagnetica

• Faraday’s resolution
• Circulation of E and the Faraday-Neumann-Lenz law
• The fictitious generator
• A framework for solving an induction problem
• Lenz’s law as an independent principle
• Lenz’s minus sign
• The alternator and the sinusoidal EMF
• When the electric field stops being conservative

19 Le equazioni di Maxwell e le onde elettromagnetiche

• The four equations (first, incomplete version)
• The displacement current
• Maxwell’s four equations
• The transformer

Z Appendice — Maturità

• Rod in a magnetic field: induction, dynamics and energy
• Key formulas: Electromagnetism