A 12.5eV electron beam is used to bombard gaseous hydrogen at room temperature What series of wavelengths will be emitted.

Explanation

`E_(n)=(-13.6)/(2^(2))eV`
Energy required to excite hydrogen atom from ground state to the second excited state
`E_("final")-E_("initial")`
`=-1.51-(-13.6)=120.9eV`
i.e., hydrogen atoms would be excited upto third energy level (i.e., n = 3) second excited state,
Alternatively

For Lyman
`(1)/(lambda)=R[(1)/(n_(f)^(2))-(1)/(n_(i)^(2))]`
or `, (1)/(lambda)=1.097xx10^(7)[(1)/(2^(2))-(1)/(3^(2))]`
`rArr lamda=122nm`
For Balmer
`(1)/(lambda)=1.097xx10^(7)[(1)/(2^(2))-(1)/(3^(2))]`
`lambda=656.3 nm`