Saved Bookmarks
| 1. |
Assume that helium obeys the Bohr theory exactly. Which of the following transitions in helium will not give rise to a spectral line which has the same wavelength as some spectral line in the hydrogen spectrum? (a) From n = 4 to n = 2 (b) From n = 6 to n = 2 (c) From n = 8 to n = 4 (d) From n = 6 to n = 3 |
|
Answer» Correct Answer is: (d) From n = 6 to n = 3 For a transition from n = p to n = q in hydrogen, the photon energy is ε1 = 13.6 (1/q2 - 1/p2) eV. For a transition from n = a to n = b in helium, the photon energy is ε2 = 4 x 13.6 (1/b2 - 1/a2) eV = 13.6 {(2/b)2 - (2/a)2} eV. For photons of the same energy to appear in the two spectra, 1/q2 - 1/p2 = (2/b)2 - (2a)2. This will be satisfied if b = 2q and a = 2p. |
|