Geertruida Luberta "Berta" de Haas-Lorentz (20 November 1885 – 1973) was a Dutch physicist and professor of the Technical University of Delft. She was the first to theoretically study thermal fluctuations in electric circuits, treating electrons as Brownian particles. Consequently she is considered one of the pioneers of electrical noise theory. She was the daughter and doctoral student of Hendrik Lorentz. She went by the name Berta, or Ber.