Question

What will be the longest wavelength line in balmer series of spectrum?

Answer 1

Since wavelength and energy are inversely related, the longest wavelength would be produced by the lowest amount of energy. That would be by the electron falling from from n = 3 (ni) to n = 2 (nf). (All Balmer series lines have nf = 2). 

Using the Rydberg equation, 

1 / lambda = R (1/nf^2 - 1/ni^2) = (1.097 x 10^7 m^-1)(1/(2^2) - 1/(3^2)) = 1.52 x 10^6 m^-1 

lambda = 1 / (1.52 x 10^6 m) = 6.56 x 10^-7 m = 656 nm

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