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Physics XII Notes for Physics Notes

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# Mechanical Waves: Important Questions

1. What do you mean by water waves?

2. Why sound produced at a distance can be heard distinctly at night than in day time?

3. Is velocity of sound more in damp air or in dry air? Explain.

4. A boat at anchor is rocked by waves whose crest is 100 feet apart and whose velocity is 25 feet /s. These reach the boats once in every t s. What is the value of t?

5. Ultrasonic, infrasonic and audio waves travel through a medium with velocity vu, vi, varespectively. Then what is the relationship among them?

6. A man stands on the ground at a fixed distance from a siren whit emits a sound of fixed amplitude.

7. The ratio of velocity of sound in hydrogen gas r=7/5 to that on helium gas r= 5/3 at the same temperature is VH:VHe, what is the value of this ratio?

8. The velocity of sound in a tube containing air at 27°C at the pressure of 760 cm of Hg is 330 m/s. What will be the velocity of sound when the pressure is increased to 100 cm of Hg and temperature is kept constant?

9. A uniform rod of length L and mass M hangs freely from a fined point. Then the velocity of transverse wave along the rod at a distance x from the free end is v m/s. What is its value?

10. In a ripple tank when one pulse is sent every 10th of a second, the distance between consecutive pulses is 30 mm. in the same depth of water pulse are produced in half second intervals. What is the distance between consecutive pulses?

11. If you are walking on the moon surface, can you hear the cracking sound behind you? Explain.

12. Do sound waves need a medium to travel from one point to other point in space? What properties of the medium are relevant?

13. Why velocity of sound in solid is more than that in liquid?

14. Why velocity of sound in liquid is more than that in air?

15. Why velocity of sound in hydrogen is more than that in air?

16. What are the draw backs of Newton’s formula for the velocity of sound in air? What is the Laplace’s correction?

17. What is the sound of clock tower heard feebly at large distance than near to it?

18. What is beat? How a musician can use this effect to tune string instrument?

19. What is threshold of hearing and threshold of pain?

20. Why are beats produced? What is beat frequency?

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

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

23. Although the density of solid is high, the velocity of sound is greater in solid, explain.

24. Why is roaring of the lion different than that of mosquito?

25. What is persistence of hearing? Also define threshold of hearing (or audibility) threshold.

26. Why is the wall at the back of the stage in a big hall made parabolic?

27. A stone is dropped from the top of the tower 300m high splashes into the water of a pond near the base, of the tower. When is the splash heard at the top? Given that the speed of sound in air is 340 m/s, g= 9.8 m/s [ ans= 8.70 s]

28. The audible frequency range of a human air is 20Hz to 20KHz. Convert this into the corresponding wavelength range. V of sound on air = 340 m/s.

29. Draw the graph for beat phenomenon.