# NCERT Physics Class 11 Exemplar Ch 15 Waves Part 3

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## Very Short Answer

18. A sonometer wire is vibrating in resonance with a tuning fork. Keeping the tension applied same, the length of the wire is doubled. Under what conditions would the tuning fork still be is resonance with the wire?

Ans: Wire of twice the length vibrates in its second harmonic. Thus if the tuning fork resonators at L, it will resonate at 2L.

19. An organ pipe of length L open at both ends is found to vibrate in its first harmonic when sounded with a tuning fork of 480 Hz. What should be the length of a pipe closed at one end, so that it also vibrates in its first harmonic with the same tuning fork?

Ans: as is constant.

20. A tuning fork A, marked 512 Hz, produces 5 beats per second, where sounded with another unmarked tuning fork B. If B is loaded with wax the number of beats is again 5 per second. What is the frequency of the tuning fork B when not loaded?

Ans: 517 Hz.

21. The displacement of an elastic wave is given by the function. Where is in cm and t is in second. Calculate the resultant amplitude.

Ans: 5cm

22. A sitar wire is replaced by another wire of same length and material but of three times the earlier radius. If the tension in the wire remains the same, by what factor will the frequency change?

Ans:

. Since frequency

23. At what temperatures (in) will the speed of sound in air be 3 times its value at?

Ans:

24. When two waves of almost equal frequencies and reach at a point simultaneously, what is the time interval between successive maxima?

Ans: