Question

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. $\frac{8R}{9}$

Answer 1

Answer: (C)

$\frac{5R}{36}$

Answer 2

Wave number $= \frac{1}{\lambda} = R\left( \frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}} \right)$

For first Balmer line n₁= 2, n₂=3

$\therefore$Wave number $= R\left( \frac{1}{2^{2}} - \frac{1}{3^{2}} \right) = R\left( \frac{9 - 4}{9 \times 4} \right) = \frac{5R}{36}$.