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Thursday, November 7

Solution For Waves Questions

Note: Correct Options are colored Ones

11) In a transverse wave the distance between the crest and the adjacent trough is
a) λ/2
b) λ/4
c) λ
d) 2λ

The difference between consecutive crests and troughs is lambda but between a crest and trough it is half of wavelength.

12) The wavelength of a wave travelling at a speed v and having frequency f is
a) v/f
b) vf
c) f/v
d) none of these

13) two waves of the same frequency and amplitude travelling in the opposite direction along the same path will form
a) electromagnetic waves
b) micro waves
c) standing waves
d) sound waves

14) A phase change of 180 is equivalent to path difference of
a) lambda/2
b) lambda
c) 2 lambda
d) 4 lambda

A phase of 2π rad is equal to path difference of λ. Since 2π rad is equal to 360 so
λ = 360 and 180 = λ/2

15) At What temp. the velocity of sound is doubled than as that 10 degree Celsius 
a) 1132 C
b) 859 C
c) 759 C
d) 283 C

Suppose at To = 10C = 283K the speed is Vo and at Tt the speed is Vt according to question we’ve to find Vt when Vt = 2Vo
According to formula

Since Vt = 2Vo and To = 283K so

16) When the wave no. of light is 5 x 106 m-1 . then its wavelength is 
a)2 x 107m
b)5 x 10

c)2 x 10-7 m


17) Wave transport energy without transporting 
c) matter

18) The speed of sound in hydrogen is _______ times its speed in oxygen
c) Four

As speed of sound is inversely proportional to the square root of density and hydrogen is 16 times lighter than oxygen so speed of sound in hydrogen is 4 times its speed in oxygen. Say speed of sound in hydrogen is VH2 and in oxygen is VO2 and their densities be ρH2 and ρO2

19) When a wave goes after collision it reflect back . Then in the result of superposition on the wave will call .
a)Longitudinal waves
b)Compressional waves
c)Stationary waves
d)Reflected waves

Speed of sound in vacuum is _________ m/s
a) 332
b) 340
c) 0
d) 350

21) For mono-atomic gas Cv=(3/2)R, therefore gamma for this is:
a) 5/3

If Cv = 3R/2 then from Cp – Cv = R the value of Cp is 5R/2

22) The velocity of wave could be increased by :
a)reducing the amplitude
b)decreasing the frequency
c)increasing the period
d)stretching the string more

Velocity is directly proportional to the square root of Tension in string

23) Energy is directly related to
a) frequency
b) wavelength
c) amplitude
d) none

24) When a wave move from denser to rarer medium which of the following quantity remains same
a) speed
b) wavelength
c) amplitude
d) frequency

25) Speed of sound is greatest in 
a) glass

Glass has more value of elastic modulus due to its atomic structure

26) Speed of sound is greatest in
a) copper

27) The frequency of the second overtone of a closed pipe is in unison with the third overtone of an open pipe other ratio of lengths of the pipe is
a) 5 : 8
b) 5: 4
c) 7: 4
d) 4: 5
e) None of these


28) During the time that sound travels 1100 feet in air, light can travel in vacuum a distance of about
a) 1100 miles
b) 200000 miles
c) 20000 miles
d) 11000 km

B is the nearest answer but logically wrong according to me. Since speed of sound is approximately 332 m/s in air. If it covers a distance of 1100 ft with a speed of 332 m/s then time taken will be 
Time = distance / speed
Now the distance is in feet let us convert it into meters as 1 foot = 0.304 meters so 1100 feet = 334 meters
So time taken is approximately 1 second.As we know that speed of light is 30,00,00,000 m/s
This means in one second it does cover a distance of 3 x 10^8 meters if you convert 3 x 10^8 meters into miles the answer is 186411.35 miles 

29) 56 tuning forks are so arranged in series, that each fork gives 4 beats/second with the previous one. If the frequency of the last fork is 3 times that of the first, then the frequency of the first fork will be
a) 55 Hz
b) 110 Hz
c) 75 Hz
d) 220 Hz

The question involves little mathematics.Let the frequency of first fork be ‘x’ and according to the question the frequency of last fork is three times the frequency of first fork i.e. 3xAs there are 56 fork and 55 beats are being produced so the frequency of last fork is given by 55*4 plus the frequency of first fork. Frequency of last fork = 3x = 55*4 + x Which gives x = 110 Hz

30) The fork A of frequency 100 Hz is sounded with another tuning fork B. the number of beats produced is 2. On putting some wax on the prong of B. the number of beats reduces to 1. the frequency of the fork B is
a) 101 Hz
b) 99 Hz
c) 102 Hz
d) 98 Hz

The frequency of fork B can be 102 Hz or 100 Hz, by loading the fork B the frequency must reduce, if frequency of B were to 102 Hz then frequency must reduce so original frequency of fork B is 102 Hz

31) A progressive wave in a stretched string has a speed of 20m/s and a frequency of 100Hz. what is the phase difference between two points 25mm part?
a) zero
b) pie/4 radian
c) pie/2 radian
d) pie radian

From speed and frequency you can calculate wavelength which comes out to be 0.2 meters or 200 mm As 200 mm gives a phase difference of 360 or 2pi rads then 25 mm will give pi/4 rads

32) which of the following statements about the stationary waves is true
a) particles between adjacent waves all have the same amplitude
b) particles between adjacent nodes are all out of phase with each other
c) particles on immediately either side of node are moving in opposite directions
d) there is minimum disturbance of the medium at the anti-node

Just imagine a stationary wave in your mind you’ll see that the nodes of adjacent waves are exactly out of phase by 180.

33) A signal has a frequency of 2 M Hz. what is the period of the signal
a) 2 us
b) 5 us
c) 200 ns
d) 500 ns

34) The amplitude of the wave is A and its intensity is I. Which amplitude is necessary for the intensity to be 2I?
a) A
b) √ A
c) √(2) x A
d) 2A


35) If Cp - Cv = R and Cp/Cv= γ, then which relation is correct
(a) Cv=R/ γ -1
(b) Cv=rR/ γ -1
(c) Cv=R
2/ γ2
(d) Cv= γ -1/R


36) when two identical travelling waves are superimposed, the velocity if the resultant wave
a) increases
b) decreases
c) remain same
d) becomes zero

Only their amplitude changes

37) if the stretching force of the wire is increased then its frequency
a) decreases
b) increases
c) remain same
d) any of the above can happen

They are directly proportional

38) A stationary wave is set up in the air column of
the closed pipe. At the closed end of the pipe
a) always a node is formed
b) always an anti-node is formed
c) neither a node nor an antinode is formed
d) sometimes a node and sometimes an antinode is formed

39) The amplitude of the sound wave is detected as its 
a) wavelength
b) frequency
c) pitch
d) resonance
e) loudness

40) if the velocity of the light in a medium depends on its frequency, then the medium is called
a) coherent
b) refractive
c) dispersive
d) diffractive
e) resonant

41) according to Laplace the sound travels in air under conditions of
a) adiabatic
b) isothermal
c) isobaric
d) isochoric

Heat of compression remains confined so no heat exchange is involved which makes it adiabatic 

42) for an echo to be heard the time difference in reaching the ear between the reflected sound waves and the sound waves travelling directly from vibrating source to ear must be
a) 0.01 sec
b) 0.1 sec
c) 1 sec
d) 10 sec
e) 100 sec

43) in order for the two sound waves to produce beats, it is important the two waves 
a) have the same frequency
b) have the same amplitude
c) have the same number of overtones
d) have slightly different frequencies
e) have slightly different amplitudes

44) a girl produce a certain note when she blows gently into an organ pipe. If she blows harder into the pipe, the most probable change will be that the sound wave
a) will travel faster
b) will have a higher frequency
c) will have a greater amplitude
d) will have a lower frequency
e) will have a lower amplitude

Sound will become louder means greater amplitude and frequency don’t depend upon speed

45) On loading the prong of the tuning fork with wax its frequency
a) decreases
b) remain same
c) increases
d) may increase or decrease

46) when the speed of sound in air is 330m/s, the shortest air column, closed at one end, that will respond to a tuning fork with a frequency of 440 vibrations per second has the length of approximately
a) 19cm
b) 33cm
c) 38cm
d) 67cm
e) 75cm

Shortest air column will be L/4 for resonance .Length of tube L can be calculated by speed and frequency 

47) if a man moves, with a speed equal to 0.5 that of sound, away from a stationary organ producing a sound of frequency f, he will probably hear a sound of frequency
a) less than f
b) f
c) 1.5f
d) 2.25f
e) 2.5f

Apply Doppler effect. But you don’t need to do any calculation as the observer is moving away from the stationary source obviously implies that frequency will decrease means it will be less than f

48) A certain stretched string produces a frequency of 1000 vibrations per second. For the same string to produce a frequency  twice as that high, the tension in the string should be
a) doubled
b) quadrupled
c) half
d) one fourth
e) square root 2 times the original

the relation between frequency and tension in stretched string is given by

49) the periodic alternation of the sound between maximum and minimum loudness are called
a) silence zone
b) interference
c) beats
d) resonance

50) the sound of a siren to the west of you is transmitted to your ear by air that is
a) vibrating in a north-south direction
b) vibrating in a south west-east direction
c) vibrating in a vertical direction
d) moving continuously westward
e) moving continuously eastward

I don’t know why the word ‘south’ is there in the option but it’s simple logic west east direction

1 comment:

  1. mistake in q 48... tension should be quadrupled to produce frequency twice to that of original one


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