3. The diagram below shows an apparatus for studying the photoelectric (PE) effect. When light of wavelength 620 nm shines on the cathode, electrons are emitted. The current I of electrons that reach the anode across a potential difference Vis measured on the ammeter A. (In what follows neglect any contact potential.) Cathode 620 mm (NA) A Anode V (volts) a. What did Einstein conclude about the nature of light in order to explain the various features of the PE effect? b. As the voltage Vis varied from negative to positive values, the current I changes as shown in the graph above. i. Why is the current of emitted electrons not zero when V