An electron in the hydrogen atom jumps from excited state 'n' to the ground state. The wavelength of the photoelectron illuminates a photo-sensitive material that has a work function - ω (in eV). The stopping potential of the photoelectron is found to be 10 eV. In a sample, electrons fall from 'n' and it is found only 2 lines belong to the visible range. Find value of the work function ω (in eV)
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Solution
As only 2 lines in visible range are emitted so, the transitions are (4→2and3→2) and n=4 Energy of photon, ΔE=13.6(112−142)eV=12.75eV So, 12.75eV=ω+ stopping potential ⇒12.75eV=ω+10eV ⇒ω=2.75eV