\ g- 



Properties of Thin Films of Platinum, 125 



are plotted to show the influence of the thickness o£ the film 



on 



(a) The actual magnitude of the currents (fig. 6) ; 

 (6) The dissymmetry (fig. 7). 



^ 











Fig 



.6. 







bCO 









1 





i 



500 









"*j|/ 







400 

 300 

 200 







£ \r 

 IK 





M 



I 



! 





|! 



.«• 







1 /R; 



9 ^ 







-i — — 



Jw 





d0 4-0 



GO 80 IOO !20 

 T*/CK/V£SS OF F/LM 



:^o Seconds 



From fig. 6 it is seen that for both sources of light there 

 is a certain thickness of film for which the photo-current 

 begins to increase rapidly, and that this thickness is the same 



Fur. 7. 



^ !• 



m 



0-8 



0-7 



f 1 



f 



\^ 









j' 







X"4 



V 



T ^ 







i 





*c*\ 



^ i 















\\ j 





















i 







N 



1 









i 



4-0 80 120 



Ttf/cK/vess cf r~/LM 



160 Seconds 



for both sources. The relative increase in current is larger 

 for the arc than for the spark. As before, a diminution of 

 the photo-currents sets in after the sudden increase. Fig. 7 

 shows that the dissymmetry is obviously a function of the 

 velocity of the electrons emitted, and that the larger the 

 velocity, the larger is the dissymmetry. Other inferences 

 that can be drawn from these results are : — 



(a) The thickness of film which makes the emergent 

 current equal to the incident is greater the greater 

 the maximum velocity of emission. 



