soMr. coxri-MfOK.tKV .iDi.ixcns is Piivsrcs ii i5'> 



electron from the atom as to remo\e any ollu-r. In the extreme 

 opjxisite case there would be as many diflerenl amounts of energy 

 recjuiretl to remove an electron from the atom as there were electrons. 

 Now, when radiation of a definite fre<iuency v falls upon a group of 

 atoms, any particular atom will cither ignore the radiation, or else 

 will absorb a definite cjuantity of energy liv from it. (The letter /;, 

 .1% iisii.il. denotes Planck's constant, G.SOlO"" ergs-seconds.) it 



Fig. 1 



follows that if an electron is extracted from an atom by this rtidiation 

 and the work W required to extract it is not exactly as great as the 

 amount liv, the difference will be turned over to the electron as kinetic 

 energy-, and the speed v with which it departs from the atom will 

 be given by the equation 



and W can be determinetl by measuring v. We can conveniently 

 refer to W as an "extraction-energy" or "extraction-potential." If 

 all the electrons occupy identical positions, W will be the same for 

 all, and the emerging electrons will all have the same spctxl. If they 

 occupy various p>ositions or "levels" as is more commonly said, there 



