548 Tables 670-672 



TABLE 670. — Electron Emission from Other Than Th-Coated Filaments 



Monatomic films of other rare earths (and alkaline earth metals absorbed on tungsten 

 and molybdenum). D cmVsec." 1 for T = 2000. Q D , heat of diffusion (g cal./g-atom), E, 

 the rate of evaporation in atoms/cm 2 sec. at 2000 K. A, bo refer to formulas on page 547. 



Emitter A 



Ce-W 8.0 



La-W 8.0 



U-W 3.2 



Yt-W 7.0 



Zr-W 5-0 



Th-W 3-0 



Th-Mo 1.5 



TABLE 671. — Photoelectric Effect 

 A negatively charged body loses its charge under the influence of ultra-violet light 

 because of the escape of negative electrons freed by the absorption of the energy of the 

 light. The light must have a wave length shorter than some limiting value X characteristic 

 of the metal. The emission of these electrons, unlike that from hot bodies, is independent 

 of the temperature. The relation between the maximum velocity v of the expelled electron 

 and the frequency v of the light is (^)mi/ t = hv — P (Einstein's equation) where h is 

 Planck's constant (6.58 X io~ 27 erg. sec.) ; hv sometimes taken as the energy of a " quanta," 

 P, the work which must be done by the electron in overcoming surface forces. (\)mir 

 is the maximum kinetic energy the electron may have after escape. Richardson identifies 

 the P of Einstein's formula with the w of electron emission of the preceding table. The 

 minimum frequency v (corresponding to maximum wave length Xo) at which the photo- 

 electric effect can be observed is determined by hv = P. P applies to a single electron, 

 whereas w applies to one coulomb (6.062 X io 23 electrons) ; therefore w = N P = .00399V0 

 ergs. <£ = (12.4X io" 5 )Xn volts. See Millikan, Proc. Nat. Acad. 2, 78, 1916; Phys. Rev. 

 7, 355, 1 916'; 4, 73, 1914; Hennings, Phys. Rev. 4, 228, 1914. 



TABLE 672. — Contact (volta) Potentials 



Pt Fe Cu Au Ag Al Mg Zn Pb Sn 



Si0 2 ...+2.22 -f-I.99 +1.60 +I.60 4-I.42 +.93 +.93 4-45 4-. 16 —.30 

 Glass ..+1.15 +1.15 +0.58 +0.58 4-0.58 -f.14 +.14 —.29 —.60 —1. 14 



Cu Cr Ta Mo Ni 



W +.08 +.11 -.38 -.21 -.17 



Si0 2 , Glass Polednik, Z. Phys 66, 619, 1930. \ 



W Kosters, " " 66, 807, 1930. J 



* Outer electron shell. f Cr, " electronegative," 2.35 ; Mn., ditto, 2.35. 



Broughall (Phil. Mag. 41, p. 872, 1921) computes in the same units from Van der Waal's 

 constant "b" the diameters of He, N, A, Kr, and X as 2.3, 2.6, 2.9, 3.1, and 3.4. These 

 inert elements correspond to Langmuir's completely filled successive electron shells. The 

 corresponding atomic numbers are 2, 10, 18, 36 and 54. For Langmuir's theory see J. Am. 

 Ch. Soc, p. 868, 1919, Science 54, p. 59, 1921, 



Smithsonian Tables 



