# Change in Frequency/Wavelength in Doppler Effect

• Samurai44
In summary, when calculating the final frequency or wavelength in Doppler effect questions, you need to consider the change in either frequency or wavelength as positive or negative based on the specific situation. Depending on whether the source is approaching or moving away, the frequency and wavelength will either increase or decrease, and this will determine the appropriate sign to use in the calculation.
Samurai44
Greetings ,
Many Doppler effect questions require to find the final Frequency/Wavelength. so after using the equation :
Δλ / λ = v / c or Δf / f = v / c
How can I know if the change in Frequency/Wavelength is positive or negative to calculate the final frequency or wavelength. because sometimes they add the change to initial but in others they subtract .

i know this's all related to :
* Δf= ff - fi or Δλ=λf - λi
* Source approaching: frequency increase , hence wavelength gets shorter
* Source moving away : frequency decrease , hence wavelength gets longer

One way to imagine this fact is to thinking about the distance. If distance get shorter then λ get shorter. Source frequency does not change but for the adapter it likes to be larger.

Samurai44
Samurai44 said:
Greetings ,
Many Doppler effect questions require to find the final Frequency/Wavelength. so after using the equation :
Δλ / λ = v / c or Δf / f = v / c
How can I know if the change in Frequency/Wavelength is positive or negative to calculate the final frequency or wavelength. because sometimes they add the change to initial but in others they subtract .

i know this's all related to :
* Δf= ff - fi or Δλ=λf - λi
* Source approaching: frequency increase , hence wavelength gets shorter
* Source moving away : frequency decrease , hence wavelength gets longer
It will depend on the situation. You need to understand various cases (there are 4 cases for sound) and pick-up the right sign.
https://s-media-cache-ak0.pinimg.com/originals/fa/4d/02/fa4d027ccc0ebeca28acd83c84aa2861.jpg

Samurai44

## 1. What is the Doppler Effect?

The Doppler Effect is the change in frequency or wavelength of a wave as it moves towards or away from an observer. This phenomenon is observed in all types of waves, including sound and light waves.

## 2. How does the Doppler Effect affect sound waves?

When a sound source is moving towards an observer, the frequency of the sound waves increases, resulting in a higher pitch. Conversely, when the sound source is moving away, the frequency decreases, resulting in a lower pitch. This change in frequency is known as the Doppler Effect.

## 3. What causes the Doppler Effect?

The Doppler Effect is caused by the relative motion between a wave source and an observer. As the source moves closer or farther away, the distance between each wave crest or trough changes, resulting in a change in frequency or wavelength.

## 4. How is the Doppler Effect used in real life?

The Doppler Effect has several practical applications, including in radar and sonar technology. It is also used in medical imaging techniques, such as ultrasound, to measure the velocity and direction of blood flow in the body.

## 5. Can the Doppler Effect be observed in light waves?

Yes, the Doppler Effect can also be observed in light waves. When a light source is moving towards an observer, the frequency of the light waves increases, resulting in a shift towards the blue end of the spectrum (known as blue shift). When the light source is moving away, the frequency decreases, resulting in a shift towards the red end of the spectrum (known as red shift).

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