A spectral line =5000 A in the light coming from a distant star i… - Vidyadip

MCQ

A spectral line $\lambda=5000 \mathring A$ in the light coming from a distant star is observed as a $5200 \mathring A$. What will be recession velocity of the star

A
$1.15 \times 10^7 cm / sec$
✓
$1.15 \times 10^7 m / sec$
C
$1.15 \times 10^7 km / sec$
D
$1.15 km / sec$

✓

Answer

Correct option: B.

$1.15 \times 10^7 m / sec$

$\Delta \lambda=5200-5000=200 \mathring A$
Now $\frac{\Delta \lambda}{\lambda^{\prime}}=\frac{v}{c}$
$ \Rightarrow v=\frac{c \Delta \lambda}{\lambda^{\prime}}=\frac{3 \times 10^8 \times 200}{5000}$$=1.2 \times 10^7 m / sec \approx 1.15 \times 10^7 m / sec$

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