$\frac{1}{\lambda}= R \left(\frac{1}{ n _1^2}-\frac{1}{ N n _2^{\frac{2}{2}}}\right) \times Z ^2$
$\therefore \frac{1}{\lambda}=1.097 \times 10^{-7}\left(\frac{1}{1^2}-\frac{1}{4^2}\right) \times 1^2$
$\therefore \frac{1}{\lambda}=1.097 \times 10^{-7} \times \frac{15}{16}\, m ^{-1}$
$\begin{aligned} \therefore \lambda =\frac{16}{1.097 \times 10^7 \times 15}\, m \\ =9.7 \times 10^{-8}\, m \end{aligned}$
$\therefore \frac{1}{2}=1. 097 \times 10^{-7}\left(\frac{1}{1^2}-\frac{1}{4^2}\right) \times 1^2$
$\therefore \frac{1}{\lambda}=1.097 \times 10^{-7} \times \frac{15}{16}\, m ^{-1}$
[આપેલ:પ્લેટીનમની દેહલી આવૃત્તિ $1.3$ $\times 10^{15} \,s ^{-1}$ અને $h =6.6 \times 10^{-34} \,J \,s$.]