Geertruida de Haas-Lorentz

Geertruida Luberta Lorentz was born on 20 October 1885 in Leiden, Netherlands, the eldest child of physicist and Nobel laureate Hendrik Lorentz and . Her siblings were: Johanna Wilhelmina (born 1889), Gerrit (born 1893, died 1894), and Rudolf (born 1895). At the time of her birth, her father was Professor of Theoretical Physics at the Leiden University. Her mother took care of the children and household, did charity work, and was heavily involved with the local women's suffrage movement. On 22 December 1910, Lorentz married Wander de Haas (who would become Professor of Experimental Physics at Leiden University), with whom she had two sons and two daughters. Some of their children changed their last name to "Lorentz de Haas." De Haas-Lorentz studied physics at Leiden University, with her father as her doctoral advisor. In 1912, she received her Ph.D. with a thesis titled ''Over de theorie van de Brown'sche beweging en daarmede verwante verschijnselen'' (On the theory of Brownian motion and related phenomena). After defending her doctoral thesis, de Haas-Lorentz taught physics at the Technical University of Delft and translated some of her father's works into German. De Haas-Lorentz died on 2 January 1973 in Leiden at the age of 87. == Research ==

De Haas-Lorentz was one the first to apply Albert Einstein's theory of Brownian motion to other domains. During her thesis work, she was the first to carry out a theoretical analysis of thermal fluctuation of electrons in electrical circuits, predating the experimental discovery of the Johnson–Nyquist noise. She considered that a circuit with resistance R and inductance L should store an energy , where I is the current. If there was a fluctuating thermal current, by the equipartition theorem the energy would be related to the thermal energy kT where k is the Boltzmann constant and T is the temperature. De Haas-Lorentz obtained, : \sqrt{\langle I^2\rangle}=\sqrt{ \frac{2 k T}{ L }}, where the angle brackets denote the thermal average. She was also the first to propose thermal fluctuations limit the detection of electromagnetic radiation. She also predicted the London penetration depth for superconductivity in 1925, before the development of the London equations in 1935. == Selected works ==

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