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Notice that the signs are different from those of the wavelength equation.
Check Your Understanding Suppose a space probe moves away from Earth at a speed 0.350 c . It sends a radio-wave message back to Earth at a frequency of 1.50 GHz. At what frequency is the message received on Earth?
We can substitute the data directly into the equation for relativistic Doppler frequency:
The relativistic Doppler effect has applications ranging from Doppler radar storm monitoring to providing information on the motion and distance of stars. We describe some of these applications in the exercises.
Explain the meaning of the terms “red shift” and “blue shift” as they relate to the relativistic Doppler effect.
What happens to the relativistic Doppler effect when relative velocity is zero? Is this the expected result?
There is no measured change in wavelength or frequency in this case. The relativistic Doppler effect depends only on the relative velocity of the source and the observer, not any speed relative to a medium for the light waves.
Is the relativistic Doppler effect consistent with the classical Doppler effect in the respect that is larger for motion away?
All galaxies farther away than about exhibit a red shift in their emitted light that is proportional to distance, with those farther and farther away having progressively greater red shifts. What does this imply, assuming that the only source of red shift is relative motion?
It shows that the stars are getting more distant from Earth, that the universe is expanding, and doing so at an accelerating rate, with greater velocity for more distant stars.]
A highway patrol officer uses a device that measures the speed of vehicles by bouncing radar off them and measuring the Doppler shift. The outgoing radar has a frequency of 100 GHz and the returning echo has a frequency 15.0 kHz higher. What is the velocity of the vehicle? Note that there are two Doppler shifts in echoes. Be certain not to round off until the end of the problem, because the effect is small.
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