The 6563 mathringA Hα line emitted by hydrogen in a star is found to be red-shifted by 15 mathringA. Estimate the speed with which the star is receding from the earth.

Question

The 6563 mathringA Hα line emitted by hydrogen in a star is found to be red-shifted by 15 mathringA. Estimate the speed with which the star is receding from the earth. (A) 343 km s -1 (B) 686 km s -1 (C) 1372 km s -1 (D) 1715 km s -1

Tardigrade Admin · Accepted Answer

(Δ u/v)=(Δ λ/λ)=(v text radial /c) ⇒ (15 mathringA/6563 mathringA)=(v text radial /3 × 108 m / s ) or v text Radial =686 km s -1

Q. The $6563 \overset{˚}{A} H_{α}$ line emitted by hydrogen in a star is found to be red-shifted by $15 \overset{˚}{A}$ . Estimate the speed with which the star is receding from the earth.

$343 km s^{- 1}$

$686 km s^{- 1}$

$1372 km s^{- 1}$

$1715 km s^{- 1}$

$\frac{Δ u}{v} = \frac{Δ λ}{λ} = \frac{v _{radial}}{c}$
$\Rightarrow \frac{15 A ˚}{6563 A ˚} = \frac{v _{radial}}{3 \times 1 0 ^{8} m / s}$
or $v_{Radial} = 686 km s^{- 1}$

Q. The 6563A˚Hα​ line emitted by hydrogen in a star is found to be red-shifted by 15A˚. Estimate the speed with which the star is receding from the earth.

343kms−1

686kms−1

1372kms−1

1715kms−1