## DOPPLER EFFECT – Class 11 | Chapter – 15 | Physics Short Notes Series PDF for NEET & JEE

Doppler Effect: The Doppler effect refers to the change in frequency and wavelength of a wave when its source and/or its observer is in motion relative to each other. The Doppler effect is most commonly associated with the change in frequency of sound waves as the source of sound and the observer move relative to each other.

For example, if a car is moving toward a stationary observer, the sound waves emitted by the car will have a higher frequency than the sound waves would have if the car were stationary. The observer would hear a higher pitched sound. Conversely, if the car were moving away from the observer, the sound waves would have a lower frequency, and the observer would hear a lower pitched sound.

The Doppler effect can also be observed with other types of waves, such as electromagnetic waves (e.g., light waves) and water waves. The mathematical expression for the Doppler effect is based on the relative velocity between the source of the waves and the observer, as well as the speed of the waves in the medium through which they are traveling.

In conclusion, the Doppler effect is the change in frequency and wavelength of a wave when its source and/or its observer is in motion relative to each other. This effect is most commonly associated with the change in frequency of sound waves, but it can also be observed with other types of waves. The mathematical expression for the Doppler effect is based on the relative velocity between the source and the observer, as well as the speed of the waves in the medium.

## Uses of the Doppler Effect

The Doppler effect has a wide range of practical applications in various fields, including:

• Meteorology: Meteorologists use the Doppler effect to measure wind speed and direction by analyzing the shift in frequency of radar waves reflected from raindrops or other particles in the atmosphere.
• Medical imaging: In medical imaging, the Doppler effect is used to measure blood flow velocity in the blood vessels by analyzing the shift in frequency of ultrasound waves.
• Astronomy: Astronomers use the Doppler effect to measure the radial velocity of stars and galaxies. This information can be used to determine the masses of these celestial bodies and to study their formation and evolution.
• Aviation: The Doppler effect is used in air traffic control to track the position and velocity of aircraft. Radars emit microwave signals that are reflected by the aircraft and the shift in frequency of these reflected signals is used to determine the velocity of the aircraft.
• Acoustics: The Doppler effect is used in acoustics to determine the speed and direction of sound waves. This information is used to study the behavior of sound waves in various environments and to design sound-proof materials and barriers.
• Seismology: Seismologists use the Doppler effect to study the movement of earthquakes. The shift in frequency of seismic waves is used to determine the velocity and direction of the movement of the Earth’s surface.

In conclusion, the Doppler effect has a wide range of practical applications in various fields, including meteorology, medical imaging, astronomy, aviation, acoustics, and seismology.

## Formula of the Doppler Effect

Due to the relative motion between the source of the sound and the observer, the doppler effect implies the apparent change in the frequency of waves. By using the following equation, we can deduce the apparent frequency in the Doppler effect.

f’ = (v ± v 0 / v  vs ) fo

Where f = frequency received by the observer

F0 = original frequency of the source

When the observer moves away from the source, the numerator is subtracted whereas the denominator is subtracted when two bodies are moving towards each other.

Wavelength (λ) = vf

## Disadvantage of the Doppler Effect

There are several disadvantages to the use of the Doppler effect:

Limitations in accuracy: The accuracy of the Doppler effect depends on various factors, including the frequency of the waves, the velocity of the source, and the angle of observation. These limitations can affect the accuracy of the results.

Complex calculations: The calculation of the Doppler effect can be complex and requires specialized equipment and software. This can limit its practical use in some fields.

Interference: The Doppler effect can be affected by interference from other sources, such as noise, static, and other radio signals. This can make it difficult to obtain accurate results.

Range limitations: The range of the Doppler effect is limited by the frequency of the waves and the power of the transmitter. This can make it difficult to use in some applications, such as in remote locations or for detecting objects at a long range.

Cost: The specialized equipment and software required for the Doppler effect can be expensive, which can limit its use in some fields.

In conclusion, while the Doppler effect has many practical applications, it also has several limitations, including limitations in accuracy, complex calculations, interference, range limitations, and cost. These limitations must be taken into consideration when using the Doppler effect for various applications.

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