Question

Why is anode maintained at a slightly negative potential wrt to grid g2?

Answer 1

The Franck–Hertz experiment was the first electrical measurement to clearly show the quantum nature of atoms, and thus "transformed our understanding of the world".[1] It was presented on April 24, 1914 to the German Physical Society in a paper by James Franck and Gustav Hertz.[2][3] Franck and Hertz had designed a vacuum tube for studying energetic electrons that flew through a thin vapor of mercury atoms. They discovered that, when an electron collided with a mercury atom, it could lose only a specific quantity (4.9 electron volts) of its kinetic energy before flying away.[4] This energy loss corresponds to decelerating the electron from a speed of about 1.3 million meters per second to zero.[5] A faster electron does not decelerate completely after a collision, but loses precisely the same amount of its kinetic energy. Slower electrons merely bounce off mercury atoms without losing any significant speed or kinetic energy.