Muhammad Umair Khan presents information on the Doppler effect. The Doppler effect is when there is an apparent change in frequency of a wave based on the relative motion between the source and observer. The document defines key terms like velocity, wavelength, and frequency. It then describes the six cases of the Doppler effect based on different motions of the source and observer. Examples of applications are given, such as using Doppler radar to measure object speed and bats using echoes to navigate.

2. Presented by: Muhammad Umair Khan
Lecturer Physics: Rangers College, Toll Plaza
M.S Management Science
MSc Applied Physics
BSc Mathematics

3. Introduction:
The Doppler effect was named after Christian Doppler, who first
came up with the idea in 1842. He learned that sound waves
would have an apparent change in frequency between the
source and observer if these are in relative motion.
Later on discovered that Doppler Effect is applicable of all types
of waves including:
 Sound Wave
 Light Wave
 Water Wave

4. Concept of Doppler’s Effect:
In order to understand Doppler’s Effect we must first know the following:
• Velocity
• Wavelength
• Frequency
Doppler’s Effect:
“The apparent change in the frequency of sound due to the relative motion between a source of
sound and a listener”

5. Concept of Doppler’s Effect
Distance covered in a definite direction is called
velocity.
v =
𝑑
𝑡
Where,
V = Velocity
d = Distance/ Displacement
t = Time
Velocity:

6. Frequency:
The rate at which something occurs over a particular
period of time or in a given sample.
𝑣 =
𝑉
λ
Where,
𝑣 = Frequency
V = Velocity
λ = Wavelength
Concept of Doppler’s Effect

7. Wavelength:
The distance between two consecutive crest or
trough is known as wavelength.
λ =
𝑉
𝑓
Where,
λ = Wavelength
v = Velocity
f = Frequency
Concept of Doppler’s Effect

8. Explanation:
Reason:
The reason for the Doppler effect is that when the source of the waves is moving towards the
observer, each successive wave crest is emitted from a position closer to the observer than the
previous wave. Therefore, each wave takes slightly less time to reach the observer than the
previous wave. Hence, the time between the arrival of successive wave crests at the observer
is reduced, causing an increase in the frequency. While they are traveling, the distance between
successive wave fronts is reduced, so the waves "bunch together". Conversely, if the source of
waves is moving away from the observer, each wave is emitted from a position farther from the
observer than the previous wave, so the arrival time between successive waves is increased,
reducing the frequency. The distance between successive wave fronts is then increased, so the
waves "spread out".

9. Cases of Doppler’s Effect
Case 1: When the listener approaches to stationary source of sound
Let a source of sound emit sound waves of frequency 𝑣 and wavelength λ given by:
λ =
𝑉
𝑣
Where,
V is the speed of sound waves
Let a listener approaches to the stationary source with a velocity of Vo
Then relative speed will be V + Vo. Frequency of sound 𝑣 heard will be:
𝒗 𝟏 =
𝑉+𝑉𝑜
λ
but λ =
𝑉
𝑣
Therefore 𝒗 𝟏 =
𝑉+𝑉𝑜
𝑉
𝑣
𝒗 𝟏 =
𝑉+𝑉𝑜
V
ₓ 𝑣
Result: Listener feels apparently greater frequency and more shrill sound.
𝒗 𝟏 = 𝟏 +
𝑽𝒐
𝑽
ₓ 𝒗

10. Case 2: When the listener moves away from a stationary source of sound
When listener moves away from a stationary source with a speed of Vo
then relative velocity of sound will be V – Vo. Frequency of the sound heard
will be
𝒗 𝟐 =
V – Vo
λ
but λ =
𝑉
𝑣
Therefore 𝒗 𝟐 =
V – Vo
𝑉
𝑣
𝒗 𝟐 =
V – Vo
V
ₓ v
Result: Listener feels apparently less frequency and more grave sound.
Cases of Doppler’s Effect
𝒗 𝟐 = 𝟏 −
𝑽𝒐
𝑽
ₓ 𝒗

11. Cases of Doppler’s Effect
Case 3: When the source of sound moves towards a stationary listener.
When source of sound moves towards stationary listener with a speed of Vs
then sound waves between listener and source are compressed, i.e. their
wavelength decreases
λ′ =
𝑉−𝑉𝑠
𝑣
Frequency of the sound heard will be:
𝒗 𝟑 =
𝑉
λ′
Therefore 𝒗 𝟑 =
V
𝑉−𝑉𝑠
𝑣
Result: Listener feels apparently greater frequency and more shrill sound.
𝒗 𝟑 =
V
V − Vs
ₓ 𝒗

12. Cases of Doppler’s Effect
Case 4: When the source of sound moves away from a stationary listener.
When source of sound moves away from a stationary listener with a speed
of Vs then sound waves between listener and source are expands, i.e. their
wavelength increases
λ′′ =
𝑉+𝑉𝑠
𝑣
Frequency of the sound heard will be:
𝒗 𝟒 =
𝑉
λ"
Therefore 𝒗 𝟒 =
V
𝑉+𝑉𝑠
𝑣
Result: Listener feels apparently less frequency and more grave sound.
𝒗 𝟒 =
V
V+ Vs
ₓ 𝒗

13. Cases of Doppler’s Effect
Case 5: When the source of sound and the listener both approaches to
each other.
If source of sound and listener moves towards each other with velocities Vs
and Vo respectively then the frequency 𝒗 𝟓 heard by the listener is given by
combining the case 1 and case 3:
In this case 𝒗 𝟓 > 𝒗
Result: Listener feels apparently greater frequency and more shrill sound.
𝒗 𝟓 =
V + Vo
V − Vs
ₓ 𝒗

14. Cases of Doppler’s Effect
Case 6: When the source of sound and the listener both moves away from
each other.
If source of sound and listener moves away from each other with velocities
Vs and Vo respectively then the frequency 𝒗 𝟔 heard by the listener is given
by combining the case 2 and case 4:
In this case 𝒗 𝟔 < 𝒗
Result: Listener feels apparently less frequency and less shrill sound.
𝒗 𝟔 =
V − Vo
V + Vs
ₓ 𝒗

15. Applications of Doppler’s Effect:
• Doppler’s Effect is used in some types of radars to measure the speed of
detected object.
• For Example radar guns.
• One of the natural applications of doppler’s effect occur in bat navigates its
flight by emitting whistles and listening for the echo.
• Meteorologists utilize Doppler effect to determine the direction and velocity
of raindrops, wind direction and other weather events.
• Satellite employs Doppler effect in its tracking techniques for determining
distance between satellite and receiver as well as time.
• Doppler effect has found its use in several other area which includes:
 Astronomy
 Vibration measurement
 To sense gesture
 Audio
 Velocity measurement