A hydrogen atom in its ground state is by light of wavelength ` 970Å Taking hc//e = 1.237 xx 10^(-6)eV m` and the ground state energy of hydrogen atom as ` - 13.6 eV` the number of lines present in the emmission spectrum is

Explanation

`E = (hc)/(lambda) = (1.237 xx 10^(-6))/(970 xx 10^(-10)) eV = 12.75 eV`
`:. `The energy of electron after absorbing this photon
`= - 13.6 + 12.75 = - 0.85eV `
This corresponds to `n = 4 `
Number of spectral line `= (n(n-1))/(2) = (4(4 - 1))/(2) = 6 `