# Acoustic Phenomena | Old is Gold | Class XII

Acoustic Phenomena
Short

1. How are beats produced? What is beat frequency?

2. What are ultrasonic and infrasonic?

3. Distinguish between ultrasonic and supersonics.

4. How it is that one can recognize a friend from his voice without seeing him?

5. Why is it roaring of a lion different than the sound of a mosquito?

6. What do you mean by the term threshold of hearing?

7. Whistle of an approaching train is shriller. Why?

8. Define beats and beat frequency.

9. Bells are made of metal and not of wood, why?

10. Explain with a figure the meaning of beats.

11. Two notes, one produced by violin and the other by a sitar, may have the frequency, yet we can distinguish between them. Why?

12. Which has a more direct influence on the sound wave: the observer is approaching the stationary sound source.

13. What is meant by threshold of hearing?

Long

1. Deduce the expressions for the frequency herd by an observer, when the observer is approaching the stationary sound source.

2. What is Doppler`s effect? Derive an expression for the apparent frequency received by a stationary observer when a source is moving away from him.

3. What do you mean by intensity and intensity level of sound? Define bel and decibel.

4. What are beats? Prove that the number of beats per second is equal to the difference between the frequencies of two superposing waves.

5. What is Doppler`s effect? Derive the change in frequency when an observer moves towards a stationary source?

6. Discuss the phenomenon of Doppler`s effect. Find the change in frequency when a moving source of sound passes a stationery observer.

7. Define intensity of sound. Show that the intensity of sound for a given frequency is directly proportional to the square of amplitude of vibration.

8. Define the intensity of sound and prove that l=1/2pVr2w2 where the symbols have their usual meaning.

9. What is the Doppler Effect in sound? Obtain an expression for the apparent frequency of the sound when the source and observer both move in the same direction.

10. Define intensity and deduce it in terms of amplitude of vibration, density of medium, angular velocity and velocity of the wave.

11. What are beats? Obtain an expression for the beat frequency when beats are produced by superposing two waves of slightly different frequencies.

12. What is Doppler`s Effect? Deduce an expression for the apparent frequency heard by a stationary observer when a source approaches towards him.

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