Effect of Potential on photoelectric current

Before I begin I just want to convey to you that please read my previous posts on photoelectric effect because it will help you understand this topic better.As,you can guess from the image itself that potential of the battery is varied in steps.Now,three conditions arise from this,so what are the three conditions??

• Collector at zero potential -The emitter in the glass tube(please refer to this post -Experimental arrangement to determine photoelectric effect) is illuminated with light of  fixed frequency and intensity I1.You will observe a small photocurrent which is due to the fact that a few electrons will reach the collector on account large velocity of emission.
• Collector at positive potential with respect to the emitter -Now vary positive potential of the collector gradually ,you will observe that photocurrent increases with increase in accelerating potential. But at a certain stage you will observe that for a particular value of positive potential photocurrent saturates.Just look at the above graph and you will be able to spot that .Now a question arises that why it became maximum and doesn't increase further when we keep on increasing accelerating potential ??It is because saturation current corresponds to a situation where all the photoelectrons emitted reach the collector junction.
• Collector at negative potential with respect to the emitter -First zero potential condition is reached then the collector is made increasingly negative gradually.At a sharply defined critical value of the negative potential photocurrent becomes zero.This is because the critical value also known as stopping potential is sufficient to repel even the most energetic photoelectron.  

Now you can intensify the experiment further by taking different intensity light but of same frequency(I3>I2>I1) .You will be able see the same results but in an elevated way,just give a thorough look at the graph you will be the master of this in no time.