Question

   Do all electrons ejected from the metal surface have the same kinetic energy? Is this important for the interpretation of this lab?

Answer 1

No it is not compulsory that all electron coming from metal surface has same kinetic energy when electron get minimum energy it get ejected from but from surface some electron at the surface they get easily ejected and some are inside so when they coming they loss some energy in collision with other electron and proton so they do not have same energy.

It is important for because it get idea about which electron first reach the other plate to flow of current.