Question

Which of the following is true for Balmer series of the hydrogen spectrum?

• A. The entire series falls in the UV region
• B. The series is partly in the visible region and partly in the UV region
• C. The wave number of the first Balmer line is $\frac{5R}{36},R$ is the Rydberg's constant
• D. The colour of the second line of Balmer series is blue.

Answer 1

Answer: (B), (C), (D)

The series is partly in the visible region and partly in the UV region.
The colour of the second line of Balmer series is blue.
Wave number $=\frac{1}{\lambda }=R\left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)$
For first Balmer line $n_1=2,n_2=3$
$\therefore$ Wave number $=R\left(\frac{1}{2^2}-\frac{1}{3^2}\right)=R\left(\frac{9-4}{9\times 4}\right)=\frac{5R}{36}$