Question

The colour of the second line of Balmer series is:

• A. blue
• B. yellow
• C. red
• D. violet

Answer 1

Answer: (A)

When an atom comes down from some higher energy level to the second energy $(n=2)$,
then the lines of spectrum are obtained in visible part and give the Balmer series. $\frac{1}{\lambda }=R\left(\frac{1}{2^2}-\frac{1}{n^2}\right),$
$n=3,4,\mathrm{5...}$ For second line $n=4$
$\therefore \frac{1}{\lambda }=R\left(\frac{1}{2^2}-\frac{1}{4^2}\right)$
$=\frac{3R}{16}$ $\Rightarrow \lambda =\frac{16}{3R}$
$R=1.097\times 10^7{m}^{-1}$
$\lambda =\frac{16}{3\times 1.097\times 10^7}$
$=4860\times 10^{-10}m$
$\Rightarrow \lambda =4860\mathring{A}$ which corresponds to colour blue.