What is the ratio of wave number of first line (lowest energy line) of Balmer series of H atomic spectrum to first line of its Brackett series?
- 5 : 1
- 5 : 0.81
- 5 : 1.75
- 5 : 27
Answer
(2) 5 : 0.81
Solution
= RH ( 1n12 - 1n22 ); the first (lowest-energy) line of a series has n2 = n1 + 1.
Balmer series (n1 = 2), first line 3 2:
B = RH ( 14 - 19 ) = 5RH36
Brackett series (n1 = 4), first line 5 4:
Br = RH ( 116 - 125 ) = 9RH400
∴ B Br = 536 4009 = 50.81
⇒ Ratio = 5 : 0.81
Answer: (2)