Question

The electron energy in hydrogen atom is given by `E_(n) = (-21.7 xx 10^(-12)/(n^(2))) erg`. Calculate the energy required to remove an electron completely from the `n = 2` orbit.What is the longest wavelength (in cm) of light can be used to cause this transition ?

Answer 1

`E_(n) = (21.7 xx 10^(-12))/(n^(2)) erg`
`:. E_(2) = (21.7 xx 10^(-12))/(4) = - 5.425 xx 10^(12) erg `
for removed of electron , `E_(2) = (hc)/(lambda)`
`E_(2)` should be given to remove electron i.e. position
`:. Lambda = (6.625 xx 10^(-27) xx 3.0 xx 10^(10))/(5.425 xx 10^(-12))`
` 366.63 xx 10^(-8) cm = 3663.6 Å`
so the longest wavelength is `3663.6 Å`