If velocity of a galaxy relative to earth is $1.2 \times 10^6 \,ms^{-1}$ then $\%$ increase in wavelength of light from galaxy as compared to the similar source on earth will be ...............$\%$
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Since $\frac{v}{c}=\frac{\Delta \lambda}{\lambda}$
$\therefore \Delta \lambda=\frac{v}{c} \times \lambda$
or $\quad \frac{\Delta \lambda}{\lambda}=\frac{1.2 \times 10^{6}}{3 \times 10^{8}}=\frac{12}{3} \times \frac{10^{5}}{10^{8}}=4 \times 10^{-3}$
$\frac{\Delta \lambda}{\lambda} \times 100=0.4$ i.e., $0.4 \%$
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