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Wave Optics

Question
CBSEENPH12038570

A hydrogen atom initially in the ground level absorbs a photon, which excites it to the n = 4 level. Determine the wavelength and frequency of photon.

Solution
Initially, hydrogen is in the ground state. 
After absorption of photon Hydrogen atom excited to level, n=4.

Energy of an electron in n
th orbit of H atom is, 

                                  En = -13.6n2eVwhen n=1;           E1 = -13.6 eV 

Energy in 4th (n = 4) level 

                  E4 = -13.642 = -0.85
             E = E4-E1

                                                       E = -0.85 - (-13.6) eV                                             = -0.85 + 13.6                                 E =12.75 eV  Now, energy of a photon = hνTherefore,                                     hv  = 12.75 eV                                 hv = 12.75 × 1.6 × 10-19J                                   v = 12.75×1.6×10-196.6 ×10-34i.e.,                                v = 3.078 ×1015 Hz, is the required frequency of the photon.Now, wavelength of photon is ,                                       λ = cλ = 3 × 1083.078 × 1015i.e.,                               λ = 974.4 Å