How can the Doppler effect of light determine an astronaut's speed?

In summary, the conversation discusses an astronaut who claimed to have seen a red light as green due to the relativistic Doppler effect while traveling at a high speed. The equation for calculating the time period is mentioned, but the correct approach for finding the speed is not clear. The suggestion to refer to the textbook for the Doppler shift equation is given.
  • #1
jessicah
3
0

Homework Statement


An astronaut is said to have tried to get out of a traffic violation for running a red light (lambda= 670nm) by telling the judge that the light appeared green (lambda= 540nm) to her as she passed by in her high powered transport. If this is true, how fast was the astronaut going?


Homework Equations



Lambda= c(Tperiod)

The Attempt at a Solution


5.40X10-7m= 3.00x108( T)
T= 1.8x10-15sec

Im not sure if this is the correct approach but once you get the time how do you get the speed?



Homework Equations





The Attempt at a Solution

 
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  • #2
Hi Jessicah, welcome to PF!:smile:

jessicah said:
5.40X10-7m= 3.00x108( T)
T= 1.8x10-15sec

Im not sure if this is the correct approach but once you get the time how do you get the speed?

Well, since this is a problem on the relativistic Doppler effect, you might try reading about the effect in your textbook and finding the equation for Doppler shift...:wink:
 

What is the Doppler effect of light?

The Doppler effect of light is the apparent shift in frequency or wavelength of light waves due to the relative motion between the source of light and the observer.

How does the Doppler effect of light work?

The Doppler effect of light works by changing the frequency and wavelength of light waves when the source of light and the observer are moving towards or away from each other. When the source moves towards the observer, the frequency of the light waves increases, making the light appear bluer. When the source moves away from the observer, the frequency decreases, making the light appear redder.

What causes the Doppler effect of light?

The Doppler effect of light is caused by the relative motion between the source of light and the observer. This can occur when either the source or the observer is moving, or both are in motion.

How is the Doppler effect of light different from the Doppler effect of sound?

The Doppler effect of light is different from the Doppler effect of sound in several ways. The most significant difference is that the speed of light is constant, whereas the speed of sound changes depending on the medium it travels through. Additionally, the Doppler effect of light is observed in the entire electromagnetic spectrum, while the Doppler effect of sound is only observed in the audible range.

What are some real-life applications of the Doppler effect of light?

The Doppler effect of light has many practical applications, including in astronomy, where it is used to determine the velocity and distance of celestial bodies. It is also used in medical imaging, such as ultrasound, to measure blood flow and detect abnormalities. In addition, the Doppler effect of light is used in police radar guns to measure the speed of moving vehicles.

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