CONTENT1. INTRODUCTION2. DOPPLER EFFECT3. WHAT IS DOPPLER EFFECT.4. DOPPLER EFFECT OF MOVING OBJECT.5. SONIC BOOM.6. OBJECT MOVING WITH SUPERSONIC SPEED.7. SOUND BARRIER8. AN AIR CRAFT MOVING WITH SPEED OF SOUND.9. RED SHIFT.
INTRODUCTION• The Doppler effect was named after Christian Doppler, who first came up with the idea in 1842. He thought that sound waves would have a higher frequency if the source was moving toward the observer and a lower frequency if the source was moving away from the observer
What is Doppler Effect• The Doppler Effect is the phenomenon observed whenever the source of wave is moving with respect to an observer .The Doppler Effect can be described as the effect produced by a moving source of wave in which there is an apparent upward shift in frequency for the observer and the source are approaching and the downward shift in frequency when the observer and the source is receding.• For-------------- EXAMPLE
TYPES OF DOPPLER EFFECT• Symmetrical:- It implies that doppler shift is same when the source of light moves towards/away from a stationary observer or the observer moves with the same velocity towards/away from the stationary source .
• Asymmetrical:- It implies that apparent change in the frequency is different when the source of sound moves towards/away from a stationary observer or as that occurs, when the observer moves with the same velocity towards/away from the stationary source .
Doppler effect for a moving objectIf object moving with a velocitythen the observer hear the frequencyof sound increasing in front of the sourceand observe frequency of sound decreasing, which is standing backward the source
WavelengthSource at Rest
Long WavelengthLow Frequency Low Pitch Ooooooo!!! Short Wavelength High Frequency High Pitch Weeeeeeeee!!! As a team, describe what happens to the wavelength, frequency, and pitch both in front of Source in Motion and behind a moving sound source.
SONIC BOOM•As you watch the animation, notice the clear formation of the Mach cone, the angle of which depends on the ratio of source speed to sound speed. It is this intense pressure front on the Mach cone that causes the shock wave known as a sonic boom
SUPERSONIC SPEED•The object which moves with speed more than the speed of sound is called the object moving with supersonicspeed
SOUND BARRIER• Jet pilots flying at Mach 1 report that there is a noticeable "wall" or "barrier" which must be penetrated before achieving supersonic speeds. This "wall" is due to the intense pressure front, and flying within this pressure front produces a very turbulent and bouncy ride.
An aircraft moving with speed of sound•If an aircraft is moving with speed of sound the sound wave which come out from it will reach to us at the same time when the aircraft come to us if the observer is in front of the aircraft.
RED SHIFT• The red shift causes lines • By measuring the amount in the spectra of galaxies of red shift in light from to be shifted towards the stars and galaxies, red end of the spectrum. astronomers can tell how More distant galaxies quickly these objects are have greater red shifts moving away from us. A than closer galaxies. The strong gravitational field red shift indicates that can also produce a red distant galaxies are shift in light; this is termed moving apart rapidly, as gravitational red shift the universe expands
• You hear the high pitch of the siren of the approaching ambulance and notice that its pitch drops suddenly as the ambulance passes you. That is called the Doppler effect.
• The speed of sound is determined by the medium in which it is traveling and therefore it is the same for a moving source. But the frequency and wavelength are changed. It is sometimes convenient to express the change in wavelength as a fraction of the source wavelength for a stationary source. The wavelengths for a moving source are given by the relationship which is given by :
An Example Of Doppler Effect• Its a common experience that when police car is coming closer then we observe that the frequency of sound is increasing & when it passes by the frequency of sound starts decreasing & when it goes very far from us our ear cant able to hear sound
HOW DOPPLER EFFECT OCCURS
When the source of sound is moving with any velocity then the number of wave remains the same but in front of thesource the waves compressed in small area & in back of the source the same no. of waves spread in larger area due to which the frequency of the sound changes and Doppler effect occurs
Altering of Doppler Effect• When a vehicle with a siren passes you, a noticeable drop in the pitch of the sound of the siren will be observed as the vehicle passes. This is an example of the Doppler effect. An approaching source moves closer during period of the sound wave so the effective wavelength is shortened, giving a higher pitch since the velocity of the wave is unchanged. Similarly the pitch of a receding sound source will be lowered.
The source have a very high speed.
The source is at rest.
The source is moving.
• There will be no Doppler effect i.e. no change in frequency in the following cases :1. If source and listener both move in the same direction with the same speed .2. When one of source /listener is at the centre of a circle while the other is moving on it with uniform speed.
APPLICATION OF DOPPLER EFFECT1. Doppler effect in light has been used to know about other galaxies in the universe. It has been found that the wavelength of the spectral line from a galaxy shows a shift towards red . By measuring the red shift the distances and velocities of various galaxies have been predicted .
2. Doppler effect has lead to the confirmation of the hypothesis that the universe is expanding .3. Doppler effect is made use of in knowing the speed of the vehicles by the traffic police .4. Doppler effect is used in RADAR( radio detection and ranging )to detect the enemies plane .