Question
$X$ different wavelengths may be observed in the spectrum from a hydrogen sample if the atoms are exited to states with principal quantum number ${n}=6$ ? The value of ${X}$ is ..... .
✓
Answer
No. of different wavelengths $=\frac{{n}({n}-1)}{2}$
$=\frac{6 \times(6-1)}{2}=\frac{6 \times 5}{2}=15$
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