] (for I line of lyman series) = 6.626 × 10−27 × 3 × 1010 × 109678 × 22 ×
3
4
= 6.54 × 10−11 erg This energy isused in liberating electron from H-atom from ground state = 6.54 × 10−11 - 13.6 × 1.602 × 10−12=4.362×10^{-11}$$ erg = 1/2 mu2 ∴ u = 3.09 × 108 cm sec−1