What are photoelectric cells?

What is photoelectric effect ? Establish Einstein's photoelectric equation with application of photoelectric effect.

What are the totipotent cells of Planaria called? (Neoblasts, Sertoli cells, Follicular cells, Helper cells)

What are Electrochemical cells ? What would happen if no salt bridge were used in electrochemical cell like Zn - Cu cell ? Write the Nernst equation to calculate the emf of this cell.