The wavelength of light observed on the earth, from a moving star… - Vidyadip

MCQ

The wavelength of light observed on the earth, from a moving star is found to decrease by $0.05 \%$. Relative to the earth the star is

A
Moving away with a velocity of $1.5 \times 10^5 m / s$
✓
Coming closer with a velocity of $1.5 \times 10^5 m / s$
C
Moving away with a velocity of $1.5 \times 10^4 m / s$
D
Coming closer with a velocity of $1.5 \times 10^4 m / s$

✓

Answer

Correct option: B.

Coming closer with a velocity of $1.5 \times 10^5 m / s$

$\frac{\Delta \lambda}{\lambda}=\frac{v}{c} \Rightarrow \frac{0.05}{100}=\frac{v}{3 \times 10^8} \Rightarrow v=1.5 \times 10 m / s$(Since wavelength is decreasing, so star coming closer)

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