Question

The wavelength of the light received from a galaxy is 0.4% greater than the wave length on the earth then the velocity of galaxy relative to the earth will be:

• A. 1.2 X ${10}^{7}m/s$
• B. 1.2 X ${10}^{6}m/s$
• C. 1.2 X ${10}^{5}m/s$
• D. 1.2 X ${10}^{4}m/s$

Answer 1

The correct option is B 1.2 X ${10}^{6}m/s$

Red shift $=({\lambda }_{Measured}-{\lambda }_{Observed})/{\lambda }_{Observed}$

Given that ${\lambda }_{Observed}=0.4$ longer than ${\lambda }_{Measured}$

$\therefore {\lambda }_{Observed}=1.004{\lambda }_{Measured}$

$\Rightarrow$ Red shift$=3.984\times {10}^{-3}$

$\therefore$ Speed$=$ Red shift $\times$Velocity of light $=3.984\times {10}^{-3}\times 3.984\times {10}^8=1.2\times {10}^{6}m/s$