The thermionic work-functions and photo-electric thresholds of the alkali metals

Abstract

That has generally been found that the thermionic currents from solids follow formula AT 1/2 e -b/T , where A and b are two constants, over a wide range temperature. So far as this matter is concerned, the same result holds if, index of T is replaced by 2, or, in fact, by any similar low number. For Sample, K. K. Smith has shown in the case of tungsten that such a formula such two constants covers the thermionic currents, from 1,050° K to 2300° K, over which range of temperature the currents increase by a factor of about 10 12 . appears, however, that the alkali metals—at any rate, under such conditions it is feasible to make experiments on them—do not subscribe to this requirement. If the old values of log i — 2 log T ( i = thermionic current, T = absolute temperature) for sodium are plotted against T -1 , it will be found that the curve not a straight line, as is the case with most substances, but is definitely convex towards the origin. This can, in fact, be seen from fig. 21, p. 539, the paper, which is a plot of log i — 1/2 log T, since this function behaves similarly to log i — 2 log T. This shows that the equation i = CT 2 e - d /T