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The 6563 Å H(2) line emitted by hydrogen...

The `6563 Å H_(2)` line emitted by hydrogen in a star is found to be red shifted by `15 Å`. Estimate the speed with which the star is receding from earth.

A

`3.2xx10^(5)ms^(-1)`

B

`6.87xx10^(5)ms^(-1)`

C

`2xx10^(5)ms^(-1)`

D

`12.74xx10^(5)ms^(-1)`

Text Solution

Verified by Experts

The correct Answer is:
B
Wavelength of `H_(alpha)"line,"lambda=6563 Ã…`
`" " = 6563xx10^(-10)m`
Red shift observed in star, `(lambda' -lambda)=15Ã…=15xx10^(-10)m`
Let the volocity of the star with which it is receding away from the earth be v
` :. ` Red shift relation, `lambda' -lambda=(v)/(c)lambda`
`:. v=(c)/(lambda)xx(lambda' -lambda)=(3xx10^(8)xx15xx10^(-10))/(6563xx10^(-10))`
` " " =6.86xx10^(5)ms^(-1)`
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