Question

What will be the longest wavelength line in Balmer series of spectrum of H-atom?
(1) 546 nm
(2) 656 nm
(3) 566 nm
(4) 556 nm​

Answer 1

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For longest wavelength in Balmer series, n2 = 3

1/λ = R[1/n1^2 - 1/n2^2]

1/λ = R[1/2^2 - 1/3^2]

1/λ = R[1/4 - 1/9]

λ = 36/(5R)

Here R = 912 A°

putting we get

λ=656 nm

It is the longest wavelength line in balmer series.