# Sound and waves practice questions / standing waves; stationary waves; waves in organ pipes and strings; doppler's effect

1) The radius, density and tension of string 'A' is twice the radius, density and tension of another string 'B'. If the length of both strings are equal, then the ratio of their frequency of vibration is:
a) 1:2                     b) 2:1
c) 1:4                     d) 4:1

2) A piano wire of diameter 0.9 mm is replaced by another wire of 0.93 mm. Then the % change in frequency of piano wire is:
a) +3.0%               b) +3.3%
c) -3.0%                d) -3.3%

3) If tension in sonometer wire decrease by 19%, then percentage change in frequency is:
a) 10%            b)-10%
c) 15%            d) -15%

4) A sonometer string and a turning fork when sounded together give 6 beats/sec whether length of sonometer string is 95 cm or 100 cm. The frequency of turning fork is:
a) 262 Hz          b) 256 Hz
c) 234 Hz           d) 260 Hz

5) With increase in temperature, frequency of sound from an organ pipe:
a) changes erratically          b) increase
c) remains unchanged        d) decrease

6) The fundamental frequency of an open organ pipe if f. If half of it is dipped into water, then new fundamental frequency will be:
a) f                 b) f/2
c) f/4              d) 2f

7) In a stationary wave, nodes are the points having
a) maximum displacement and maximum strain
b) maximum displacement and minimum strain
c) minimum displacement and minimum strain
d) minimum displacement and maximum strain

8) In a stationary wave antinodes are the points having:
a) maximum displacement and maximum strain
b) maximum displacement and minimum strain
c) minimum displacement and minimum strain
d) minimum displacement and maximum strain

9) At open end of an organ pipe
a) an antinode is always produced
b) a node is always produced
c) either antinode or node may be produced
d) neither node nor antinode is produced

10) The fundamental frequency of a closed organ pipe is f. The frequency of its first overtone is:
a) f                       b) 2f
c) 3f                     d) f/2

11) As a empty vessel is filled with water its frequency
a) increase
b) decrease
c) remains unchanged
d) none of these

12) A tube, closed at one end and containing air produces, when excited, the fundamental note of frequency 512Hz. If the tube is open at both ends, the fundamental frequency that can be excited is (in Hz)
a) 1024                   b)512
c) 256                     d)128

13) An object producing a pitch of 400 Hz approaches a stationary person in a straight line with a velocity of 200m/s. Velocity of sound is 300m/s. The person will note a change in frequency as the object flies past him equal to
a) 1440 Hz                 b) 240 Hz
c) 1200 Hz                 d) 960 Hz

14) An engine is moving on a circular track of radius 100m with the speed 20m/s. What will be the frequency observed by an observer standing stationary at the centre of the circular path when the engine blows a whistle of frequency 500 Hz?
a) >500 hz                   b) <500 hz
c) 500 hz                     d) No sound

15) When both source and observer approach each other with a velocity equal to half of the velocity of sound, the change in frequency of sound as detected by the listener is:
a) 0%                     b) 200%
c) 50%                   d) 150%

16) A source of sound produces waves of λ=40cm in air. It is moving with a velocity one-fourth the velocity of sound towards east. The apparent wave length noted by a man in opposite direction is:
a) 30 cm              b) 60 cm
c) 50 cm              d) 70 cm

17) At what speed should a source of sound move so that observer finds the apparent frequency equal to half of the original frequency:
a) v/2                     b) 2v
c) v/4                     d) v

18) A galaxy is approaching the earth with a velocity of 105m/s. As observed on the earth, the shift in the spectral line of wave length 5700Å will be
a) 1.9Å                  b) 3.8Å
c) 0.53Å                d)1.06Å

19) Two whistles A and B produce notes of frequencies 660 Hz and 596 Hz respectively. There is listener at the middle of the line joining them. Now the whistle B and the listerner start moving with the speed 30 m/s away from the whistle A. If the speed of the sound is 330m/s, how many beats will be heard by the listener?
a) 2                   b) 4
c) 6                   d) 8

20) A whistle of frequency 500 Hz is tied to a end of a string of length 1.2m revolves at 400 rev/min. A listerner standing some distance away in the plane of rotation of whistle hears frequencies in the range:
a) 436 to 574           b) 426 to 586
c) 426 to 574           d) 436 to 586

21) In the spectrum of light of a luminous heavenly body, the wave length of spectral line is measures to be 4747 λ while actual wavelength of the spectral line is 4700 λ. Then relative velocity of heavely body w.r.t earth is
a) 3×105 m/s, towards the earth
b) 3×105 m/s, away from earth
c) 3×106 m/s, towards earth
d) 3×106 m/s, away from earth

22) The wavelength of light observed on the earth, from a moving star is found to decrease by 0.05% relative to the earth, the star is:
a) moving away with a velocity of 1.5×10m/s
b) moving closer with a velocity of 1.5×10m/s
c) moving away with a velocity of 1.5×10m/s
d) moving towards with a velocity of 1.5×10m/s

Answers :-
1) a  2) d  3) b  4) c  5) b  6) a  7) d  8) b  9) a  10) c  11) c  12) a  13) d  14) c  15) b  16) c  17) d  18) a  19) b  20) d  21) d  22) b

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