= Richardson hot-wire emission experiment
{c}
In his Nobel lecture, delivered on 12 December 1929 for the 1928 prize, <Owen Willans Richardson> recalled heating wires for weeks while hand-pumping away gas released by the apparatus. With <platinum>, he found a finite emission per unit area that rose rapidly with <temperature>. His initial 1901 formula used $T^{1/2}$; he preferred the $T^2$ form in 1911.<Nobel Lectures, Physics 1922–1941/Thermionic Phenomena and the Laws which Govern Them by Owen Willans Richardson>[Nobel Lectures, Physics 1922–1941; pp. 224–225 and 229, preparation and chronology]{ref}
The early apparatus surrounded a heated <platinum> wire with a metal cylinder connected to earth through a <galvanometer>. Wire <electrical resistance> supplied the <temperature> readout. After checking collection saturation, Richardson measured at a wire potential of $-120\,\mathrm V$, over roughly $1300$–$1600\,\mathrm K$; reversing polarity suppressed the negative discharge.<Histories of the Electron: The Birth of Microphysics edited by Jed Z. Buchwald and Andrew Warwick/O. W. Richardson and the Electron Theory of Matter, 1901–1916 by Ole Knudsen>[Histories of the Electron: The Birth of Microphysics edited by Jed Z. Buchwald and Andrew Warwick; pp. 229–231, resistance thermometry and Fig. 7.2, reproducing the 1903 apparatus]{ref}
\Image[/thermionic-emission-hot-wire-collector.png]
{title=Heated-wire emission and separate collection and temperature measurements}
{description=Original functional schematic of the measurement principle, with a wire and surrounding collector shown in section. The layout is simplified; no dimensions or instrument performance are asserted.}
The inference rests on several controls. A <temperature> sweep probes thermal escape; reversing the collecting <electric field> tests the sign of the mobile <electric charge>; varying collection voltage tests whether transport is limiting. Prolonged pumping and heating test whether a transient gas release is responsible. These controls address different alternatives, and none by itself establishes a clean, uniform surface.
For a modern repetition, stabilize each <temperature>, measure the collector <electric current> against collecting <electric potential difference>, and record the pressure and surface preparation. Repeat selected <temperatures> after cooling to reveal drift. Use the collection plateau and the actual emitting area to construct a <Richardson plot>. The resulting slope estimates the <work function> only within the stated surface and transport assumptions; it does not turn an uncontrolled wire into a reference material.
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