AP EAMCET Engineering 20 Apr 2019 Shift 1 Paper

In a photoelectric experiment, a monochromatic light is incident on the emitter plate E. as shown in the figure. When switch S1 is closed and switch S2, is open, the pliotoelectrons strike the collector plate C with a maximum kinetic energy of 1 eV. If switch S1 is open and switch S2, is closed and the frequency of the incident light is doubled, the pliotoelectrons strike the collector plate with a maximum kinetic energy of 20 eV. The threshold wavelength of the emitter plate is