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BELL SYSTEM TECHNICAL JOURNAL 



sorbs the amount hv of energy from the beam. Through this absorp- 

 tion, an electron is detached from the atom. If however the electrons 

 were merely separated from the atom and left stationary beside it, the 

 energy of the system (ion plus electron) would by definition have been 

 augmented merely by Wi. This quantity is (by our supposition) less 

 than hv. However the entire energy hv has been absorbed; the differ- 

 ence {hv — Wi) is likewise transferred to the ion-plus-electron system, 

 in the form of kinetic energy of the liberated electron. The electron 

 flies away with speed F, determined by the relation 



\mVr^hv-Wi. 



(7) 



The foregoing paragraph contains several interlocking assumptions, 

 which if they are all true lead to this conclusion : When a beam of radia- 

 tion of frequency v falls upon a layer of atoms having ionizing-energies Wu 

 TF2, . . . Wi . . . , electrons of various speeds spring ojtt of the layer, 



U1 



\/////////////// A 



\///////////////A 



Fig. 6 



there being for each value of W, a corresponding group of electrons of which 

 the speed is given in terms of W by equation (7). 



Suppose that one irradiates a metal with high-frequency radiation, 

 and by a system of slits confines his experimentation to electrons pro- 

 jected in directions nearly normal to the metal surface, and applies a 



