Doppler Effect Flashcards
What is the Doppler effect?
It is the change in frequency of the sound detected by a listener because the sound source and listener have different velocities relative to the medium of sound propagation
What happens if the sound source moves towards the listener ?
The frequency detected by the listener will be higher than the frequency at the source
What happens if the sound source moves away the listener?
The detected frequency will be the less than the frequency at the source of the sound
What causes the detected frequency to increase?
The distance between the crests of the wavelengths decreases resulting in the compression of sound waves thus a higher frequency
What causes the detected frequency to decrease?
As the distance between sound waves increases, the frequency of the the waves goes down and the wave length goes up.
What sign is used when the source of the sound is moving towards the listener?
When the source moves towards the listener the detected frequency is higher therefore we use -Vs
What sign do we use when the sound source is moving away from the listener?
The detected frequency decreases, so we will use +Vs in the denominator
What sign do we use when the listener moves towards the source of the sound?
The perceived frequency increases therefore we use + Vo
What sign do we use when the listener moves away from the sound source?
When the listener moves away, the perceived frequency decreases therefore we use -VL
What causes the red shift and the blue shift ?
This phenomenon is causes by the gradual increase or decrease of the frequency of light detected by observers on earth by the stars
When does red shift occur?
The red shift occurs when stars move further away from the earth due to the expansion of the universe.
When does blue shift occur?
Blue shift occurs when the stars move closer to the Earth
Why do stars appear blue when they move closer to earth ? 🌎
This is because the light emitted by them is compressed resulting in a higher frequency and a lower wavelength.
Why do the stars appear more red as they move further away from the earth ?
They appear red because the light emitted by the stars is being stretched resulting in longer / higher wavelengths and lower frequency
