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The 6563Å Halpha line emitted by hydroge...

The `6563Å Halpha` line emitted by hydrogen in a star is found to be redshifted by `15Å`. Estimate the speed with which the star is receding from the Earth.

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Use the formula `lambda.-lambda=(v)/(c)lambda`
i.e., `v=(c)/(lambda)(lambda.-lambda)=(3xx10^(8)xx15)/(6563)=6.68xx10^(5)ms^(-1)`
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