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Measurement of the electron charge by a vacuum diode

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 obtained values of the electron charge differs 0.11 × 10−19 C and 0.01 × 10−19 C from the currently accepted value e = 1.6021766208(98) × 10−19 C.