16.Rest mass of an electron is 0.51 MeV. If it is given a velocity of 0.8 c, its kinetic energy will be

17.Rest mass of a photo is

18.If photons of 60 nm are incident on hydrogen, then max. K.E. of the emitted electrons will be

19.When distance between a monochromatic source and photo cell is 20 cm, then cut off voltage and saturation currents are 0.6 volt and 18.0 mA respectively . If distance between the two is increased to 60 cm, then

20.When a monochromatic point source of light is at a distance of 0.2 m from a photoelectric cell, cut off voltage and the saturation current are respectively 0.6 V and 18.0 mA. If same source is placed 0.6 m away from the photoelectron cell, then