Question

A star is moving away from the earth with a velocity of 100 km/s. If the velocity of light is $3 \times 10^{8}m/s$ then the shift of its spectral line of wavelength 5700 Å due to Doppler's effect will be.

• A. 0.63 Å
• B. 1.90 Å
• C. 3.80 Å
• D. 5.70 Å

Answer 1

Answer: (B)

1.90 Å

Answer 2

$\Delta\lambda = \lambda\frac{v}{c} = 5700 \times \frac{100 \times 10^{3}}{3 \times 10^{8}} = 1.90Å$