Doppler Effect of light ; and electric , magnetic fields

In summary, the electric and magnetic fields don't change their structure even when they are not stationary, i.e., they don't stretch or squeeze. So how is the phenomenon of Doppler Effect of light observed? What does it mean for a field to squeeze or stretch? I don't understand the terms you are using or the connections you are trying to make.
  • #1
A Dhingra
211
1
my query is : The electric and magnetic fields don’t squeeze or stretch then how is Doppler Effect of light possible?

In the phenomenon of Doppler Effect, light emitted from a moving source is detected to have different frequency. If this is taken on terms of detecting the no. of waves passing through the detector in one second it is fine. But according to the principle of relativity, the speed of light is a constant …. It does not change even if its source is moving…. And that means if still Doppler Effect is observed then the frequency, say, has got increased, then the wavelength should decrease to keep the speed of light constant. And as the wavelength appears to decrease though the original emitted one is larger….. it can be visualized as the wave has got squeezed due to its motion. But electric and magnetic fields don’t change their structure even when they are not stationary, i.e., they don’t stretch or squeeze….. Then how is the phenomenon of Doppler Effect of light observed?
 
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  • #2
What does it mean for a field to squeeze or stretch? What has squeezing or stretching to do with the Doppler effect? I don't understand the terms you are using or the connections you are trying to make.
 
  • #3
by squeeze and stretch , i mean the shape and structure of the field lines which don't change.
... when the electric charge is in motion, its motion does not affect the shape of the fields, that is, the field is dragged with the charge without getting the distance between the consecutive field lines change.( though that distance is already very small or negligible...)

and the connection is that ,as they remain unaffected, how is Doppler effect possible which calls for the wavelength to change...in a way causing the field lines to get affected by motion...
 
  • #4
A Dhingra said:
by squeeze and stretch , i mean the shape and structure of the field lines which don't change.
... when the electric charge is in motion, its motion does not affect the shape of the fields
This is incorrect. The motion of a charge very much affects the shape of the fields that it generates. The equation governing that is called the Liénard–Wiechert fields:

http://en.wikipedia.org/wiki/Liénard–Wiechert_potential
http://fermi.la.asu.edu/PHY531/larmor/index.html

As you can see, the Lienard Wiechert fields are not at all the same as the static field given by Coulomb's law.

In the end, the Doppler effect for light happens the same way as the Doppler effect for sound. To first order, if a wave of frequency f traveling at c is emitted by an object traveling at v then the distance between successive peaks is not c/f but (c±v)/f and therefore the received frequency for a stationary receiver is different from f. Do you understand the Doppler effect for sound?
 
  • #5
Last edited:

1. What is the Doppler Effect of light?

The Doppler Effect of light is the change in frequency and wavelength of light waves when an observer or source of light is in motion relative to each other. This causes a shift in the perceived color of the light.

2. How does the Doppler Effect of light affect astronomy?

The Doppler Effect of light is used in astronomy to determine the motion and distance of celestial objects. By analyzing the shift in the wavelength of light emitted by stars and galaxies, scientists can determine their velocity and distance from Earth.

3. What is the difference between the Doppler Effect of light and sound?

The Doppler Effect of light and sound both involve a shift in frequency and wavelength, but the key difference is that light is an electromagnetic wave while sound is a mechanical wave. This results in different equations and applications of the Doppler Effect for each.

4. How does the Doppler Effect of light apply to the color of stars?

The Doppler Effect of light can cause a shift in the color of stars, known as redshift or blueshift. If a star is moving away from Earth, the light waves will be stretched and appear redder, while a star moving towards Earth will have its light waves compressed and appear bluer.

5. Can the Doppler Effect of electric and magnetic fields be observed?

Yes, the Doppler Effect can also apply to electric and magnetic fields. When an observer or source of the fields is in motion, there will be a change in the frequency and wavelength of the fields, similar to the Doppler Effect of light. This is often observed in electromagnetic radiation, such as radio waves.

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