20. A photoelectric cell is made using emitting material with a work function of 2.00 eV. A constant voltage difference V is maintained between the emitting surface and the collecting surface in a direction to push electrons back towards the emitting surface. When the wavelength of the radiation is changed, the longest wavelength which produces a photocurrent is 350 nm. Calculate the voltage difference V. Answer in volts. (A) 5.55 (B) 7.55 (C) 8.55 (D) 3.55 (E) 1.55