Advertisements
Advertisements
प्रश्न
Discuss the following case-
Observer in motion and Source at rest.
- Observer moves towards Source
- Observer resides away from the Source
Advertisements
उत्तर
(a) Observer moves towards Source:
Observer moves towards Source
We can assume that the observer O moves towards the source S with velocity vo. The source S is at rest and the velocity of sound waves (with respect to the medium) produced by the source is v.
From the Figure, It is observed that both vo and v are in opposite direction. Then, their relative velocity is vr = v + vo. The wavelength of the sound wave is λ = `"v"/"f"`, which means the frequency observed by the observer O is f ‘ = `"v"_"r"/lambda`. Then
`"f"' = "v"_"r"/lambda = (("v" + "v"_0)/"v")"f"`
`= "f"(1 + "v"_0/"v")` ...(7)
(b) Observer recedes away from the Source:
If the observer O is moving away (receding away) from the source S, then velocity v0 and v move in the same direction. Hence, their relative velocity is vr = v – v0. Hence, the frequency observed by the observer O is
`"f"' = "v"_"r"/lambda = (("v" + "v"_0)/"v")"f"`
`= "f"(1 - "v"_0/"v")` ...(8)
APPEARS IN
संबंधित प्रश्न
State the expression for apparent frequency when listener is stationary and source is moving towards the listener.
Answer briefly.
State the expression for apparent frequency when source of sound and listener are
- moving towards each other
- moving away from each other
How do animals sense impending danger of hurricane?
Two cars moving in opposite directions approach each other with speed of 22 m/s and 16.5 m/s respectively. The driver of the first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is [velocity of sound 340 m/s]: ____________.
A source of sound is moving with constant velocity of 30 mis emitting a note of frequency 256 Hz. The ratio of frequencies observed by a stationary observer while the source is approaching him and after it crosses him is ______. (speed of sound in air = 330 m/s)
A train whistling at constant frequency is moving towards a station at a constant speed V. The train goes past a stationary observer on the station. The frequency n ′ of the sound as heard by the observer is plotted as a function of time t (figure). Identify the expected curve.
A train standing at the outer signal of a railway station blows a whistle of frequency 400 Hz still air. The train begins to move with a speed of 10 ms–1 towards the platform. What is the frequency of the sound for an observer standing on the platform? (sound velocity in air = 330 ms–1)
In a quink tube experiment, a tuning fork of frequency 300 Hz is vibrated at one end. It is observed that intensity decreases from maximum to 50% of its maximum value, as tube is moved by 6.25 cm. Velocity of sound is ______ m/s.
The observer is moving with velocity 'v0' towards the stationary source of sound and then after crossing moves away from the source with velocity 'v0'. Assume that the medium through which the sound waves travel is at rest. If v is the velocity of sound and n is the frequency emitted by the source, then the difference between apparent frequencies heard by the observer is ______.
The pitch of the whistle of an engine appears to drop by 20% of its original value when it passes a stationary observer. If the speed of sound in the air is 350 m/s, then the speed of the engine (in m/s) is ______.
