29. Light from an astronomical source is found to be shifted to a one pe rcent l
ID: 2106099 • Letter: 2
Question
29. Light from an astronomical source is found to be shifted to a one pe rcent lower frequency than had the source been at rest. What radial ve locity could cause such a shift?A. 3.0×10^7 m/s moving away from the observer B. 3.0×10^6 m/s moving away from the observer C. 3.0×10^6 m/s moving toward the observer D. 1.5 ×10^6 m/s moving toward the observer E. 1.5×10^6 m/s moving away from the observer 29. Light from an astronomical source is found to be shifted to a one pe rcent lower frequency than had the source been at rest. What radial ve locity could cause such a shift?
A. 3.0×10^7 m/s moving away from the observer B. 3.0×10^6 m/s moving away from the observer C. 3.0×10^6 m/s moving toward the observer D. 1.5 ×10^6 m/s moving toward the observer E. 1.5×10^6 m/s moving away from the observer
Explanation / Answer
the relativistic doppler factor is
Fs/F0 = sqrt[(1-beta)/(1+beta)]
where beta = v/c
Fs= 99%*F0 =0.99*F0
(1-beta)/(1+beta) =0.9801
1- beta = 0.9801 +0.9801*beta
0.0199 =1.9801*beta
beta =0.010049997
V = c*beta
V = 3.015*10^6 m/s
The shift is toward lower frequencies (red shift), it means the source is moving away from the observer.
Correct answer is B)