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Doppler effect

Hello there!

Let me explain you in very simple words, i.e to explain it to a laymen

When the distance between you and any wave, say sound wave, is decreasing you will hear more clearly or loudly. On the other hand if the distance between you and the wave is increasing you will hear faint sound.

Let me be a little formal.

Something you should know here is,



Now Concentrate, The image here describe the case, A person (observer) in the middle observing two police mobiles (source of wave), one is on the left & the other is on right, as that car (from right) coming nearer to person the frequency or the no. of waves per second are higher as compared to the car (left side) going far from the person observing it.

Doppler effect is always observed when either the source or the observer is moving relatively & thus it state that

When a source or the observer is moving relative to each other there is a shift in frequency, in easy words there is a change in no. vibrations/waves observed.

If the distance between the source & observer is decreasing the frequency does increase, the frequency would be decreasing if the distance between the source and the observer is increasing.

There are many examples we observe (specially related to sound waves) in daily life, e.g.

  • listening to siren of Ambulance (when it come nearer to us we observe higher frequency result in a loud sound & vice versa)
  • or Police mobile as I mentioned above
  • piercing sound of a flying aircraft

But when I say word ‘Wave’ this mean any wave, even light waves gives Doppler effect.

The concept of “Universe is Expanding” was understood with the help of Doppler Effect. Yes!

As we’ve said above the Doppler effect is actually the shifting of frequency while an observer or source of wave is moving relatively. When we explain this effect in terms of Astronomy, a term “Red Shift” (i.e shifting towards red, or getting more red) is used. You should remember that Red light has the least frequency in the visible region (i.e VIBGYOR). As our Universe is expanding the signal observed from the galaxies & stars (which are source of light) lowering its frequency time to time, which means that these objects are going far from us, by which we concluded that Our Universe is Expanding. Correct?

So I just tried to explain it philosophically not mathematically so that any person could understand this.

Hope the explanation was enough to give you a basic idea about the effect. Detailed explanation with mathematical formulation will be posted soon. Don’t forget to give your feedback below, Thank You!


* Image copied from Google

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No. of vibrations/waves per second observed.

As the image below says,red light have least no. of waves whereas violet have the maximum no. of waves, which simply mean that here red light has the lowest frequency in the visible region and violet got the highest.


* Image copied from Wikipedia.