An electron in a hydrogen atom falls from n equals 3 to n equals 2. The energy of the emitted photon is about

  • A. 1.89 eV
  • B. 13.6 eV
  • C. 10.2 eV
  • D. 3.4 eV

Explanation

The n equals 3 level is at minus 1.51 eV and n equals 2 at minus 3.4 eV, so the difference is 1.89 eV, a red photon and the first line of the Balmer series. The value 10.2 eV belongs to the n equals 2 to n equals 1 transition, in the ultraviolet. Always subtract the two level energies rather than quoting either one alone.

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