Doppler's Effect Presented by : - Dr.R.K.Mishra PGT(Phy) JNV, Tenughat Bokaro, Jharkhand.

Doppler's Effect

• Presented by : -

Dr.R.K.Mishra

PGT(Phy)

JNV, Tenughat

Bokaro, Jharkhand

CONTENTCONTENT1. 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

• 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

What is 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 .

TYPES OF DOPPLER EFFECT

• 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 .

If object moving with a velocity then the observer hear the frequency of sound increasing in front of the source and observe frequency of sound decreasing, which is standing backward the source

Doppler effect for a moving object

Source at Rest

Wavelength

Source in Motion

Short Wavelength

High Frequency

High Pitch

Weeeeeeeee!!!

Long Wavelength

Low Frequency

Low Pitch

Ooooooo!!!

As a team, describe what happens to the wavelength, frequency, and pitch both in front of 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 BARRIERSOUND BARRIER

• Jet pilots flying at Mach 1 report Jet pilots flying at Mach 1 report that there is a noticeable "wall" or that there is a noticeable "wall" or "barrier" which must be penetrated "barrier" which must be penetrated before achieving supersonic before achieving supersonic speeds. This "wall" is due to the speeds. This "wall" is due to the intense pressure front, and flying intense pressure front, and flying within this pressure front produces within this pressure front produces a very turbulent and bouncy ride. a very turbulent and bouncy ride.

An aircraft moving with speed of sound

•If an aircraft is moving with If an aircraft is moving with speed of sound the sound speed of sound the sound wave which come out from it wave which come out from it will reach to us at the same will reach to us at the same time when the aircraft come time when the aircraft come to us if the observer is in to us if the observer is in front of the aircraftfront of the aircraft..

RED SHIFT

• The red shift causes lines in the spectra of galaxies to be shifted towards the red end of the spectrum. More distant galaxies have greater red shifts than closer galaxies. The red shift indicates that distant galaxies are moving apart rapidly, as the universe expands

• By measuring the amount of red shift in light from stars and galaxies, astronomers can tell how quickly these objects are moving away from us. A strong gravitational field can also produce a red shift in light; this is termed gravitational red shift

• 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 :

EQUATIONEQUATION

An Example Of Doppler Effect

•It's 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 can't 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 the

source 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

SONIC BOOM

• When a vehicle with a siren passes When a vehicle with a siren passes you, a noticeable drop in the pitch of you, a noticeable drop in the pitch of the sound of the siren will be the sound of the siren will be observed as the vehicle passes. This observed as the vehicle passes. This is an example of the Doppler effect. is an example of the Doppler effect. An approaching source moves closer An approaching source moves closer during period of the sound wave so during period of the sound wave so the effective wavelength is the effective wavelength is shortened, giving a higher pitch since shortened, giving a higher pitch since the velocity of the wave is the velocity of the wave is unchanged. Similarly the pitch of a unchanged. Similarly the pitch of a receding sound source will be receding sound source will be loweredlowered.

Altering of Doppler Effect

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 EFFECT

1. 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 .