An electron in the hydrogen atom jumps from excited state n to the ground state. The wavelength so emitted illuminates a photosensitive material having work function 2.75eV. If the stopping potential of the photoelectron is 10V, the value of n is
Einstein’s photo-electric equation is given by, eV0 = hν - φ0…(1)
where e is electronic charge, V0 is stopping potential, h is plancks constant, ν is frequency of radiation and φ0 is work function .
if we consider hν as the difference between energy En of nth excited state and ground state(n=1), we rewrite eqn.(1) as
En = eV0 + φ0 = 10+2.75 = 12.75 eV …(2)
Energy difference En between nth excited state and ground state is given by,
from (2) and (3), we have
solving for n in eqn.(4), we get n = 4