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Q.
A star is moving away from earth and shift in spectral line of wavelength $5700\,\mathring{A}$ is $1.90 \,\mathring{A}$. Velocity of the star is :
Wave Optics
Solution:
By Doppler's effect in light shift in wavelength is given as
$\Delta \lambda=\frac{v}{c} \lambda $
$\Rightarrow v=\frac{c \Delta \lambda}{\lambda} $
$\Rightarrow v=\frac{3 \times 10^{8} \times 1.9 \times 10^{-10}}{5700 \times 10^{-10}}$
$=100\, km \,s ^{-1}$