Category Archives: Electron-Beam Tube

Javier De Elias Cantalapiedra from Madrid, Spain posted the YouTube video above to show the e/m measurement system that he put together based on the description in our book.  His measurement system is based on Hoag’s method, and his nicely laid-out setup allowed him to obtain very nice results (4 to 6% error compared to the theoretical e/m).

Javier is an industrial engineer who works in the telecommunications industry.  However, his passion is physics, which he pursues at a (very high) amateur level.

Thank you Javier for sharing!

Figure 54 in the book shows our setup based on a 6AF6-G “magic eye” tuning tube to measure e/m.  The pictures in this figure supplement the book’s Figure 54 to help you build your own system.   In the 6AF6, electrons produced by a thermionic cathode cause fluorescence on the tube’s anode. Applying an external magnetic field curves the path of the electrons reaching the anode’s fluorescent coating. Knowing R and the voltage applied to the tube allows one to calculate e/m. Continue reading→

Figures 51 and 52 in the book show how to use an oscilloscope 2AP1 CRT to measure e/m using Hoag’s method.  The pictures in this figure supplement the book’s, showing you how to construct the d.i.y. setup, as well as the way in which the electron beam fan is reduced to a point as the magnetic field fulfills the focusing equation.  In this setup, an AC signal is placed across one set of plates of the CRT to produce a line on the screen. The solenoid is then energized until the line makes one complete helical turn. Continue reading→