Practice portal › Atoms › Hydrogen Spectrum and Transitions
Asked in GSEB Board July 2015 · Number of spectral lines
Given: a ground-state hydrogen atom (E₁=-13.6 eV) absorbs 12.1 eV.
Energy after absorption: E=-13.6+12.1=-1.5 eV.
From Eₙ=-(13.6)/(n²) eV: n²=(13.6)/(1.5)≈9, so the atom is now in n=3.
Idea: one atom returns to the ground state either in a single jump or in steps, giving one photon per jump.
Direct route 3→1: one photon. Stepwise route 3→2→1: two photons.
So one atom emits 1 or 2 photons. (Across many atoms all three lines 3→1, 3→2 and 2→1 appear, but that counts lines, not the photons from one atom.)
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