Question

Light coming from a star is observed to have a wavelength of 3737 Å, while its real wavelength is 3700 Å. The speed of the star relative to the earth is [Speed of light $= 3 \times 10^{8}m/s$]

• A. $3 \times 10^{5}m/s$
• B. $3 \times 10^{6}m/s$
• C. $3.7 \times 10^{7}m/s$
• D. $3.7 \times 10^{6}m/s$

Answer 1

Answer: (B)

$3 \times 10^{6}m/s$

Answer 2

By using $\Delta\lambda = \lambda\frac{v}{c}$ ⇒ (3737-3700)= $3700 \times \frac{v}{3 \times 10^{8}}$

⇒ $v = 3 \times 10^{6}m/s$.