Question

Earth is moving towards a stationary star with a velocity $100{\text{kms}}^{-1}$. If the wavelength of light emitted by the star is $5000{\text{A}}^o$, then the apparent changes in wavelength observed by the observer on earth will be

• A. $0.67{\text{A}}^o$
• B. $1.67{\text{A}}^o$
• C. $16.7{\text{A}}^o$
• D. $167{\text{A}}^o$

Answer 1

The correct option is B $1.67{\text{A}}^o$

According to the Doppler effect in light,

$\Delta \lambda =\frac{v\lambda }{c}=\frac{{10}^5\times 5000{\text{A}}^o}{3\times {10}^8}=1.67{\text{A}}^o$

Option 'B' is correct.