question_answer

The ground state energy of hydrogen atom is \[-13.6\text{ }eV.\] The photon emitted during the transition of electron from n = 3 to n = 1 state, is incident on a photosensitive material of unknown work function. The photoelectrons are emitted from the materials with a maximum kinetic energy of 9 eV. The threshold wavelength of the material used is ____\[\overset{\text{o}}{\mathop{\text{A}}}\,\].  

Answer:

4000