Q. The ionisation potential of hydrogen atom is $- 13.6\ eV$. An electron in the ground state of a hydrogen atoms absorbs a photon of energy $12.75\ eV.$ How many different spectral line can one expect when the electron make a downward transition?

A) 1
B) 4
C) 2
D) 6
Explanation

(d) $E\ = \ E_{1}/n^{2}$
Energy used for excitation is 12.75 eV
$ie,$ $( - 13.6\ + 12.75)\ eV\ = \ - \ 0.85\ eV$
Energy levels of H-atom
The photon of energy 12.75$\ eV$ can excite the fourth level of H-atom
Therefore, six lines will be emitted.
$\left( n\frac{(n - 1)}{2}\ lines \right).$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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