Question

Given the value of Rydberg constant is $10^7 \, m^{-1}$, the wave number of the last line of the Balmer series in hydrogen spectrum will be :

• A. $0.5 \times 10^7 \, m^{-1}$
• B. $0.25 \times 10^7 \, m^{-1}$
• C. $2.5 \times 10^7 \, m^{-1}$
• D. $0.025 \times 10^4 \, m^{-1}$

Answer 1

Answer: (B)

$\frac{1}{\lambda } = RZ^{2} \left(\frac{1}{n_{2}^{2}} - \frac{1}{n_{1}^{2}}\right) = 10^{7} \times1^{2} \left(\frac{1}{2^{2}} - \frac{1}{ \infty^{2}}\right)$
$ \Rightarrow $ wave number $= \frac{1}{\lambda } = 0.25 \times10^{7} m^{-1} $