Q.

Hydrogen atom in ground state is excited by a monochromatic radiation of λ = 975 Å. Number of spectral lines in the resulting spectrum emitted will be     [2014]

1 3  
2 2  
3 6  
4 10  

Ans.

(3)

Energy of the photon, E=hcλ

  E=6.63×10-34×3×108975×10-10J

     =6.63×10-34×3×108975×10-10×1.6×10-19eV=12.75 eV

After absorbing a photon of energy 12.75 eV, the electron will reach the third excited state of energy -0.85 eV, since the energy difference corresponding to n=1 and n=4 is 12.75 eV.

   Number of spectral lines emitted=n(n-1)2=4(4-1)2=6