Doppler's Effect
• Presented by : Dr.R.K.Mishra
PGT(Phy)
JNV, Tenughat
Bokaro, Jharkhand
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CONTENT
INTRODUCTION
DOPPLER EFFECT
WHAT IS DOPPLER EFFECT.
DOPPLER EFFECT OF MOVING OBJECT.
SONIC BOOM.
OBJECT MOVING WITH SUPERSONIC SPEED.
SOUND BARRIER
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
object
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
Wavelength
Source at Rest
Long Wavelength
Low Frequency
Low Pitch
Ooooooo!!!
Short Wavelength
High Frequency
High Pitch
Weeeeeeeee!!!
Source in Motion
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 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
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 :
EQUATION
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
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 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 .