Question

A star is moving away from earth with velocity of $100 \, km \, s^{- 1}$ . If the velocity of light is $3\times 10^{8} \, m \, s^{- 1}$ , then shift of the spectral line of $\lambda =5700 \, Å$ due to Doppler effect will be

• A. $1.90 \, Å$
• B. $3.80 \, Å$
• C. $5.70 \, Å$
• D. None of these

Answer 1

Answer: (A)

In case of Dopplers effect in light waves
Using $\Delta \lambda =\frac{\upsilon}{c}\times \lambda =\frac{10^{5} \times 5700}{3 \times 10^{8}}=1.90 \, Å$
$\Delta \lambda =$ shift to spectral line