Emission transitions in the Paschen series end at orbit `n = 3` and start from orbit n and can be represented as `v = 3.29 xx 10^(15) (Hz) [1//3^2 - 1//n^2]` . Calculate the value of n if the transition is observed at 1285 nm. Find the region of the spectrum.

Explanation

`v = (c)/(lamda) = (3.0 xx 10^(8) ms^(-1))/(1285 xx 10^(-9) m) = 3.29 xx 10^(15) ((1)/(3^(2)) - (1)/(n^(2)))`
or `(1)/(n^(2)) = (1)/(9) - (3.0 xx 10^(8) ms^(-1))/(1285 xx 10^(-9) m) xx (1)/(3.29 xx 10^(15)) = 0.111 - 0.071 = 0.04 = (1)/(25) or n^(2) = 25 or n = 5`
The radiation corresponding to 1285 nm lies int eh infrared region.