The measurement of the electron charge is a suitable experimental assignment for high-school and
undergraduate courses of physics. We used two vacuum electron-tubes: (a) a double rectifying modern
diode with an indirectly heated cathode and (b) a specially prepared double diode with a directly
heated cathode and thermocouple. There was a small retarding potential between the cathode and
anode, which gave an opportunity to assume Maxwell’s distribution of the velocities of the emitted
electrons for the measurement of the electron charge. The electrical scheme for this measurement is
simple and common electronic devices can be used. We obtained the value for the electron charge
(1.491 ± 0.036) × 10 −19 C if measured on the common commercial double diode vacuum-tube with the
use of an optical pyrometer and (1.611 ± 0074) × 10 −19 C if measured on the specially prepared
double diode vacuum-tube using a thermocouple to determine the cathode temperature. The obtain…