THE ALKALI METAL PHOTOELECTRIC CELL 



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spherical anode and concentric spherical cathode are shown in Figure 5. 

 The rate at which saturation is approached with voltage varies with 

 the wave length of the exciting light. The longer the wave length, 

 the slower the electrons, as shown above, and the more quickly are 

 they captured by the central anode. 



When gas is introduced into a central anode cell, we again have 

 ionization bv collision, and the voltage-current curve is turned upward 



WOLTS ON CATHODE "VOLTS ON CATHODE 



Fig. 5 — Voltage-current curves for typical central anode vacuum cell. 



100 i 



+V0LT5 ON CATHODE - V0LT5 ON CATHODE 



Fig. 6^Voltage-current curves for t^-pical central anode gas filled cell. 



from the voltage axis in the manner shown in Figure 6. As in the case 

 of the central cathode cells, the current increases with voltage until 

 the critical potential for the gas is reached. 



The illumination-current relationship is rectilinear in the central 

 anode cells, as it was in the central cathode cells, provided the pre- 

 cautions as to avoiding free glass surfaces, already mentioned, are 

 observed. 



