Question

The longest wavelength in Balmer series of hydrogen spectrum will be

• A. $6557\stackrel{\text{o}}{A}$
• B. $1216\stackrel{\text{o}}{A}$
• C. $4800\stackrel{\text{o}}{A}$
• D. $5600\stackrel{\text{o}}{A}$

Answer 1

Answer: (A)

The longest wavelength in Balmer series of hydrogen spectrum occurs in third orbit. The relation for Balmer series is given by $\frac{1}{\lambda }=R\left[\frac{1}{2^2}-\frac{1}{3^2}\right]$ $=R\left[\frac{1}{2^2}-\frac{1}{3^3}\right]$ (where R has the value $1.098\times {10}^7$ per metre) $=\frac{5}{36}\times 1.098\times {10}^7$ $\lambda =\frac{36\times {10}^{-7}}{5\times 1.098}$ $=6557\stackrel{\text{o}}{A}$