4.) Answer all parts ) Briefly explain the operating principle of a photo emissive cell b) i. What would be the charge delivered to the anode by a single photon detected by a 14-stage photomultiplier (PM) having a stage gain (gain for a single stage) of 3.7? Assume that one electron is produced by a photon. The charge of electron = 1.6 x 10-19 C. ii. Write down the advantages and limitations of a photomultiplier c) What are the two modes that a photodiode can be used? Compare the advantages and disadvantages of each mode