Question

The wavelength of $H_{\alpha }$ line in the hydrogen spectrum is found to be $6563 \, Å$ in the laboratory. If the velocity of the milky way is $1.05\times 10^{6} \, m \, s^{- 1}$ , then the wavelength of $H_{\alpha }$ line in the spectrum of milky way will be

• A. $6457 \, Å$
• B. $6586 \, Å$
• C. $7123 \, Å$
• D. $7349 \, Å$

Answer 1

Answer: (B)

As $\lambda =\Delta \lambda \times \frac{c}{v}$ or $\Delta \lambda =\lambda \times \frac{v}{c}$
$\Delta \lambda =\frac{6563 \times 1.05 \times 10^{6}}{3 \times 10^{8}}Å=2297\times 10^{- 2}$
$=22.97 \, Å\approx 23 \, Å$
$\therefore $ New wavelength is $\left(6563 + 23\right) \, Å$
$=6586 \, Å$