doppler effect - Overview, Structure, Properties & Uses

Doppler Effect - Definition, Formula, Examples, Uses, FAQs

Edited By Team Careers360 | Updated on May 30, 2022 05:23 PM IST

After reading this article, the reader should be able to understand the following- Doppler effect, doppler effect definition, blue shift, doppler effect in light formula, doppler effect in sound, apparent frequency, doppler effect example etc.

Doppler effect-

Before going into the science of it, let us look at our daily experience. Have you ever noticed an ambulance passing by with the sound of its siren? The sound of the siren is audible as long as it is close to you and diminishes with increasing distance. Well, this is the doppler effect.

Doppler effect meaning- Doppler effect is described as either decrease or an increase in the wavenumber of the source with respect to the observer i.e., you, who is at the receiving end of the frequency.

Doppler effect definition- It is defined as an apparent change in the frequency with the respect to the observer. This change in frequency is termed as Doppler shift.

In 1842, Austrian physicist Johann Doppler established the relation between emitted frequency and observed frequency. He called this change in frequency a doppler shift.
Both longitudinal waves and transverse waves show the Doppler effect. The whole universe is obeying the doppler effect. Edwin Hubble was the first scientist to notice that the whole universe is expanding as a consequence of the doppler effect.
Longitudinal waves are associated with sound objects. Transverse waves are associated with light.

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It is easy to imagine a transverse wave. Shake a jute rope from one of its ends, it will start to vibrate in a perpendicular direction. This is the movement of a transverse wave. However, a longitudinal wave is a little hard to imagine because the movement takes place in 3- dimensions. When spring is pressed, vibration occurs at regular intervals. This wave is a longitudinal wave.

doppler frequency is the apparent frequency that is either increased or decreased from the original frequency of the source.

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Doppler frequency is given as –

f=(c±v')/(c±v'') f'

Above written formula is the Doppler effect equation.

where f is the observed frequency due to the doppler effect.

f'is the original frequency of the source.

v' is the velocity of the observer

v'' is the velocity of the source

However, this might come to you as a surprise that the observed frequency has nothing to do with the distance between the source of the wave and the object at the receiving end of the wave. The Doppler effect does not depend upon the distance joining the observer and the source of the wave.

The Doppler effect in the light formula/doppler effect formula for light is exactly the same as the doppler effect formula for sound waves/doppler shift formula ultrasound. It is also called the doppler equation.

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Application of doppler effect in sound and light-

Applications of the Doppler effect in sound, as well as light, are unlimited. Doppler effect has found its applications in the field of chemistry, physics, astronomy, medicine, robotics, etc.

What is doppler effect used for?

Some of the uses of the Doppler effect-

Doppler effect in light waves-

Blueshift definition- When the frequency of a source is increased as compared to its previous frequency with respect to the receiver it is defined as blue shift.

Redshift definition- When the frequency of a source is decreased as compared to its previous frequency with respect to the receiver it is defined as redshift.

Blueshift and redshift are the two terms used to denote frequency shift in the case of light waves. The spectrum of electromagnetic waves has waves from highest to lowest frequencies. The speed of galaxies and stars is measured using the doppler principle. If the frequency emitted by a star is decreased then it is denoted as redshift. Red because red has the highest wavelength or lowest frequency in visible spectra. If the frequency emitted by the source is increased with respect to its original frequency it is said to have blue shifted.

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An increase in frequency means that the star has moved closer to Earth.

However, it should be noticed that there is not an actual change in the frequency emitted by the source, it only appears to have changed with respect to the object that is why it is called apparent frequency or Doppler frequency.
Doppler effect is used to determine the valence state of elements like iron and molybdenum in Mossbauer spectroscopy. A source is attached to a wheel at a very low temperature and gamma rays are emitted by this source. A doppler shift is calculated.
Doppler effect police radar is observed. In this case, the fading sound of a police vehicle as it moves away from you is the doppler effect.
Robots take the help of the Doppler effect in estimating their proximity to objects or tracking any obstacles.
Objects can be detected with the help of radar by using the same doppler effect. Doppler effect in radars is the most common application of Doppler shift.

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Limitations of the doppler effect-

Imagine the object and source of the frequency are both at rest.

Then according to the doppler effect equation-

f=(c±v')/(c±v'') f'

v’= 0 (at rest)

v’’= 0 (at rest)

f=c/c f'

f=f'

Therefore, in the case when both the observer and source of a sound wave are at rest the frequency of sound for the receiver and source will be the same.

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Frequently Asked Question (FAQs)

1. Give any 5 doppler effect examples.

Doppler effect is applicable for light as well as sound waves.
Most people get confused about the applicability of the doppler effect in light waves.
RADAR uses the doppler effect in the detection of objects and obstacles.
Doppler effect is applicable while we are waiting for a bus, an ambulance passes us by. We listen to the diminishing sound of the siren while it goes away from us.
In Medicine, doctors use the doppler principle by using an echocardiogram to analyze blood flow velocity at any particular time.
In submarines, the doppler effect is used to calculate the speed
In astronomy, the speed of galaxies and stars is estimated by using the doppler principle.

2. Give Blue Shift definition.

Blueshift is defined as the increase in frequency and therefore, a decrease in the wavelength of source with respect to the observer. It is called Blue because in the visible spectrum blue color has the highest frequency and hence low wavelength.

Blueshift is used to determine the velocities with which the galaxies and stars are moving.

3. What is the doppler effect?

Doppler effect is the shift in frequency of sound sources with respect to the observer. Doppler effect is observed in sound as well as a light wave. It was given by Johann Doppler in 1842.

Write the apparent velocity definition.

The apparent velocity is the true velocity when the surface is parallel to the refractor.

4. Define the doppler effect and the doppler principle.

Doppler principle states that there is a shift in the original frequency of the objects in the point of the observer. This new frequency is known as apparent frequency. This shift in frequency is given by-

f=(c±v')/(c±v'') f'

Where v’ is the frequency of the observer and v’’ is the frequency of the wave.

5. What are the limitations of the doppler effect?

Limitations of the doppler effect are as follows-

The velocity of the observer and source of the wave should not be at rest.

If the velocity of sound and observer is greater than the velocity of light, the doppler effect will not be observed.