# The Doppler Effect: Why is the Second Wave of Light Different?

• Manraj singh
In summary: Also, the shift is relatively small compared to other factors that can affect color perception, such as lighting and the color of the car itself. In summary, the Doppler effect does occur with electromagnetic waves, but it is not noticeable to the human eye in this scenario.
Manraj singh
I was watching a video on the doppler effect by edx.org. The video said that the second wave of light given out, when the star(the light emitting object in this case) moves towards you, is not as big as the first one. So, it does not extend beyond the original wave. Why does this happen?

We would need a reference to the video; your description is not at all clear - if that is exactly what they said, I am unable to understand what they mean.

So please clarify.

i mean when the source is in motion, why doesn't the black circle go beyond the red one, or the green circle beyond the blue one?

Manraj singh said:
why doesn't the black circle go beyond the red one,
Because they propagate at the same speed.

Both waves are extending at the same rate and the inner one never catches up to the first because it was emitted later (just as my younger brother will never be as old as I am because he was born later and we age at the same rate.)

Oh. Thanks. But in the case of the car if the car were to accelerate, would it happen?

If the car accelerates to a speed that is smaller than the speed of sound, The inner spheres will shift even more but remain inside the outer spheres. If the car reaches speeds higher than the speed of sound the spheres start to overlap producing a sonic boom.

That actually would be cool. Thanks

dauto said:
If the car reaches speeds higher than the speed of sound the spheres start to overlap producing a sonic boom.

I've always heard of sonic booms that happen when an object moves faster than the speed of sound but how and why exactly does it happen? Can you clarify it a little bit ??

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ElmorshedyDr said:
I've always heard of sonic booms that happen when an object moves faster than the speed of sound but how and why exactly does it happen? Can you clarify it a little bit ??
Nice animation here:
http://en.wikipedia.org/wiki/Sonic_boom

A.T. said:
Yeah, that's a good animation, I already realize that the object moves faster than the sound waves that it produces, but why does this cause the BOOM that we hear ?

If a sound source is moving faster than the speed of sound the wave crests will start overlapping each other. They interfere constructively leading to a very intense but brief sound perceived as a sonic boom.

dauto said:
If a sound source is moving faster than the speed of sound the wave crests will start overlapping each other. They interfere constructively leading to a very intense but brief sound perceived as a sonic boom.
Cool ! thanks, that's understood! Does Doppler effect happen to E.M waves ?

ElmorshedyDr said:
Cool ! thanks, that's understood! Does Doppler effect happen to E.M waves ?

yes

that how police radar ( well all radar works ) to specifically determine speed of an object

EDIT: I should also add LIDAR, Laser radar ... again, speed determination using doppler

Dave

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Since we are on the topic can someone also explain why a cloud is formed around the object crossing the sound barrier?

dauto said:
If a sound source is moving faster than the speed of sound the wave crests will start overlapping each other. They interfere constructively leading to a very intense but brief sound perceived as a sonic boom.

ElmorshedyDr said:
Cool ! thanks, that's understood! Does Doppler effect happen to E.M waves ?

For the electromagnetic wave equivalent of a "sonic boom", look up "Cherenkov radiation".

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/cherenkov.html

http://en.wikipedia.org/wiki/Cherenkov_radiation

So is this because there is so much pressure exerted on the moisture that it condenses?

Manraj singh said:
So is this because there is so much pressure exerted on the moisture that it condenses?

not quite, read the first paragraph in that wiki link again

" The condensation is caused by the sudden change in pressure across the shock waves"

Dave

Hi guys
I've a question,that is why for example when a source of sound get closer to an observer with the same speed as an observer get closer to a source of sound the frequancy that observer heard is not same?
Please help me

Why doesn't the color of cars change with respect to the observer due to Doppler effect ??

ElmorshedyDr said:
Why doesn't the color of cars change with respect to the observer due to Doppler effect ??

The light actually does doppler shift up or down in frequency depending on the motion of the cars. The issue is that our eyes and brain are simply not sensitive enough to notice the change.

## 1. What is the Doppler Effect?

The Doppler Effect is a phenomenon in which the frequency of a wave appears to change when the source of the wave is in motion relative to the observer. This effect can be observed in various types of waves, including sound waves and light waves.

## 2. How does the Doppler Effect apply to light waves?

The Doppler Effect applies to light waves in the same way as it applies to sound waves. When a source of light is moving towards an observer, the wavelength of the light appears shorter, resulting in a higher frequency and a shift towards the blue end of the spectrum. Conversely, when the source is moving away from the observer, the wavelength appears longer, resulting in a lower frequency and a shift towards the red end of the spectrum.

## 3. Why is the Doppler Effect important in understanding the second wave of light?

The Doppler Effect is important in understanding the second wave of light because it helps to explain why the light from a moving source appears to have a different wavelength and frequency than the light from a stationary source. This effect allows scientists to determine the speed and direction of a source of light in relation to an observer.

## 4. How does the Doppler Effect relate to the concept of redshift and blueshift?

Redshift and blueshift are both examples of the Doppler Effect in action. These terms are used to describe the shifting of light towards the red or blue end of the spectrum, respectively, due to the relative motion of the source and observer. Redshift is observed when an object is moving away from the observer, while blueshift is observed when an object is moving towards the observer.

## 5. What are some real-world applications of the Doppler Effect?

The Doppler Effect has many practical applications in various fields. It is commonly used in weather forecasting to track the movement of storms and in astronomy to measure the speed and distance of celestial objects. It is also used in medical imaging, such as ultrasound, to detect the flow of blood and other fluids in the body. In addition, the Doppler Effect is utilized in radar technology for tracking the speed of moving objects, such as aircraft and vehicles.

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