Q 12-10-113JEE MainJEE Main 2021 (20 Jul, Shift 2)Easy
With what speed should a galaxy move outward with respect to earth so that the sodium-D line at wavelength 5890 Å is observed at 5896 Å?
Answer: (A) 306 km sec$^{-1}$
$v = c\dfrac{\Delta\lambda}{\lambda} = 3\times10^5\times\dfrac{6}{5890} \approx 306\ \text{km s}^{-1}$
Solution by Sreeraj P, M.Sc Physics