Question

The wavelength of the first spectral line in the Balmer series of hydrogen atom is 6561 A. The wave length of the second spectral line in the Balmer series of singly ionized helium atom is 

(1) 1215 Å 

(2) 1640 Å 

(3) 2430 Å 

(4) 4687 Å 

Answer 1

Correct option : (1) 1215 Å

Explanation :

We know that Balmer series terminates at n = 2. Hence the first spectral line of Balmer series corresponds to transition from n₁ = 3 to n₂ = 2. Hence we have

The second line of Balmer series of ionzied helium atom corresponds to transition from n₁ = 4 to n₂ = 2