Most Important Long Question :::::
What is Doppler Effect ? Discuss its different cases.
Answer:::
Definition;
The change in the frequency of waves due to relative motion between the source and observer is called Doppler's Effect.
Example:
1). The frequency of whistle of Train coming towards the platform appears to become higher to an observer standing on the platform .
2).The frequency of whistle of Train going away from the platform appears to become lower to an observer standing on the platform.
V=Fλ
یہاں پر ہم نے (Frequency) کو find کرنا ہے
F= V ➡(1)
λ
CASE :- 1
When observer moves towards stationary source
V=Fλ
F= V ∴ V=V+Uo
λ
FA=V+Uo ∴ λ=V/F
λ
FA= V+Uo
V/F
FA=[ V+Uo ]F
V
∴V+Uo>1
V
FA>F
CASE:-2
When observer moves away from stationary source.
V=Fλ
F= V ∴ V=V+Uo
λ
FB=V-Uou ∴ λ=V/F
λ
FB= V-Uo
V/F
FB=[ V-Uo ]F
V
∴V-Uo <1
FB<F V
CASE:- 3
When source is moving toward stationary observer
V=Fλ
F= V
λ
λ = V ∴ V=V-Us
F
λc=V-Us →(¡)
F
λc =V - Us
F F
λc=λ -△λ ∴ △=Doppler shift
∴V=Fλ
Fc = V
λc
From equation 1
Fc= V
V-Us
F
Fc=[ V ]F ∴ V >1
V-Us V-Us
Fc>F
CASE:- 4
When source is moving away from stationary observer.
V=Fλ
F= V
λ
λ = V ∴ V=U+Us
F
λD=V+Us →(¡)
F
λD=V + Us
F F
λD=λ -△λ ∴ △=Doppler shift
∴V=Fλ
FD = V
λc
From equation 1
FD= V
V+Us
F
FD=[ V ]F ∴ V <1
V+Us V+Us
FD<F
............Long Complete ...........