Consider a gas consisting `Li^(+2)` (which is hydrogen like ion).
(a) Find the wavelength of radiation required to excite the electron in `Li^(++)` from `n=1` and `n=3`. (Ionisation energy of the hydrogen atom equals `13.6 eV`).
(b) How many spectral lines are observed in the emission spectrum of the above excited system?

Answer

(a) `(hc)/(13.6xx8e)=113.7Å` (b) `3`

Explanation

(a) `DeltaE= 13.6xx3^(2)xx((1)/(1)(1)/(3^(2)))eV`
`13.6xx8eV`
`lambda=(hc)/(DeltaE)=(12400)/(13.6xx8)Å=113.7Å`
(b) no. of spectral lines `= .^(n)C_(2)`
`= .^(3)C_(2)=3`