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प्रश्न
The 6563 Å Hα line emitted by hydrogen in a star is found to be redshifted by 15 Å. Estimate the speed with which the star is receding from the Earth.
उत्तर
Wavelength of `"H"_alpha` line emitted by hydrogen,
λ = 6563 Å
= 6563 × 10−10 m
Star’s red-shift, (λ' − λ) 15 Å = 15 × 10−10 m
Speed of light, c = 3 × 108 m/s
Let the velocity of the star receding away from the Earth be v.
The red shift is related with velocity as:
`lambda"'" - lambda = "v"/"c" lambda`
`"v" = "c"/lambda xx (lambda"'" - lambda)`
= `(3 xx 10^8 xx 15 xx 10^(-10))/(6563 xx 10^(-10))`
= 6.87 × 105 m/s
Therefore, the speed with which the star is receding away from the Earth is 6.87 × 105m/s.
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