Q. In terms of Rydberg’s constant $R$, the wave number of the first Balmer line is
A) $R$
B) $3R$
C) $\frac{5R}{36}$
D) $\frac{8R}{9}$
Explanation
(c) 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 $= R\left( \frac{1}{2^{2}} - \frac{1}{3^{2}} \right) = R\left( \frac{9 - 4}{9 \times 4} \right) = \frac{5R}{36}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.