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The Doppler Effect refers to the change in frequency or wavelength of a wave as observed by an observer moving relative to the wave source, applicable to sound, light, and electromagnetic waves. It is commonly illustrated by the changing pitch of a siren as an emergency vehicle approaches or recedes, and is crucial in astronomy for measuring the movement of celestial bodies through redshift and blueshift. The effect has various applications, including radar, medical imaging, and navigation systems.

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14 views3 pages

Document 12

The Doppler Effect refers to the change in frequency or wavelength of a wave as observed by an observer moving relative to the wave source, applicable to sound, light, and electromagnetic waves. It is commonly illustrated by the changing pitch of a siren as an emergency vehicle approaches or recedes, and is crucial in astronomy for measuring the movement of celestial bodies through redshift and blueshift. The effect has various applications, including radar, medical imaging, and navigation systems.

Uploaded by

lesniklesnik1357
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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📘 Class Notes: The Doppler Effect

Date: June 27, 2025

Subject: Physics

Topic: The Doppler Effect

Instructor: [Insert Name]

🔍 Definition

The Doppler Effect is the change in frequency or wavelength of a wave


in relation to an observer who is moving relative to the wave source.

🌊 Applies To:

 Sound waves
 Light waves
 Electromagnetic waves in general

🎵 Everyday Example (Sound):

 When a car or ambulance passes by, its siren pitch changes.


o Approaching = higher pitch (frequency increases)
o Receding = lower pitch (frequency decreases)

🌌 Doppler Effect in Light:

 Redshift: Light source moving away → Wavelength increases,


frequency decreases
 Blueshift: Light source moving toward → Wavelength decreases,
frequency increases
 Important in astronomy to measure the movement of stars and
galaxies

🧮 Formula:

For sound (approximate, when source speed is much less than wave
speed):

f′=f(v±vov∓vs)f' = f \left(\frac{v \pm v_o}{v \mp v_s}\right)

Where:

f′f' = observed frequency


ff = emitted frequency

vv = speed of the wave in the medium


vov_o = speed of observer (positive if moving toward source)


vsv_s = speed of source (positive if moving toward observer)



🧠 Key Concepts:

 No Doppler effect if both source and observer are stationary.


 Greater relative speed = greater frequency shift.
 Works with any type of wave (not just sound!).

🔬 Applications:

 Radar and speed detection (police radar guns)


 Astronomy (measuring expansion of universe)
 Medical imaging (Doppler ultrasound)
 Navigation systems (Doppler radar)

📎 Fun Fact:

The Doppler Effect was named after Christian Doppler, who proposed it
in 1842 to explain the color of binary stars.

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