# Doppler Effect

### What is Doppler Effect?

It's the apparent change in the frequency of a wave caused by relative motion between the source and the observer

### Doppler effect Cases:- (The general relationship of observed frequencies)

Here how to determine the signs of the above law

See This Video For more clarification:- How To Solve Doppler Effect Physics Problems - Basic Introduction

### Doppler effect cases:- (In Detail)

Case 1:- the observer is moving/ the sound source is static (Source Speed = zero)

• If the observer moves toward the static sound source (Then the observed frequency is greater than the source frequency)

(In this case:- Let's say that the sound wave takes originally 3 seconds to travel from the source until it reaches the observer, if the observer moves toward the source, then the sound wave will actually take less than 3 seconds to reach the observer)

• If the observer is moving away from the static sound source (Then the observed frequency is less than the source frequency)

(In this case:- Let's say that the sound wave takes originally 3 seconds to travel from the source until it reaches the observer, if the observer moves away from the source, then the sound wave will actually take more than 3 seconds to reach the observer)

Case 2:- the observer is static/ the audio source is moving (Observer Speed = zero)

• If the sound source moves toward the static observer (Then the observed frequency is greater than the source frequency)

(In this case:- you will hear the sound waves closer than if the source is static because the wavelength measured by the observer will be shorter than the source wavelength)

• If the sound source moves away from the static observer (Then the observed frequency will be less than the source frequency)

(In this case:- you will hear the sound waves farther than if the source is static because the wavelength measured by the observer will be longer than the source wavelength)

### The Doppler effect also occurs in electromagnetic waves:-

• Stars that move toward Earth tend to be blue
• Stars that move away from Earth tend to be red