CBSE Class 11 Physics Waves MCQs Set B

Question: In the sonometer experiment, a tuning fork of frequency 256 Hz is in resonance with 0.4 m length of the wire when the iron load attached to free end of wire is 2 kg. If the load is immersed in water, the length of the wire in resonance would be (specific gravity of iron = 8)
a) 0.37 m
b) 0.43 m
c) 0.31 m
d) 0.2 m
Answer: a

Question: Two strings A and B, made of same material, are stretched by same tension. The radius of string A is double of radius of B. A transverse wave travels on A with speed vA and on B with speed vB. The ratio vA / vB is
a) 1/2
b) 2
c) 1/4
d) 4
Answer: a

Question: A string is stretched between two fixed points separated by 75.0 cm. It is observed to have resonant frequencies of 420 Hz and 315 Hz. There are no other resonant frequencies between these two. The lowest resonant frequency for this string is :
a) 205 Hz
b) 10.5 Hz
c) 105 Hz
d) 155 Hz
Answer: c

Question: Two identical piano wires kept under the same tension T have a fundamental frequency of 600 Hz. The fractional increase in the tension of one of the wires which will lead to occurrence of 6 beats/s when both the wires oscillate together would be
a) 0.02
b) 0.03
c) 0.04
d) 0.01
Answer: a

Question: A wave of frequency 100 Hz travels along a string towards its fixed end. When this wave travels back, after reflection, a node is formed at a distance of 10 cm from the fixed end. The speed of the wave (incident and reflected) is
a) 20 m/s
b) 40 m/s
c) 5 m/s
d) 10 m/s
Answer: a

Question: A source of sound gives 5 beats per second, when sounded with another source of frequency 100 second^–1. The second harmonic of the source, together with a source of frequency 205 second^–1 gives 5 beats per second. What is the frequency of the source?
a) 105 second^–1
b) 205 second^–1
c) 95 second^–1
d) 100 second^–1
Answer: a

Question: A source of unknown frequency gives 4 beats/s, when sounded with a source of known frequency 250 Hz. The second harmonic of the source of unknown frequency gives five beats per second, when sounded with a source of frequency 513 Hz. The unknown frequency is
a) 246 Hz
b) 240 Hz
c) 260 Hz
d) 254 Hz
Answer: d

Question: A closed organ pipe (closed at one end) is excited to support the third overtone. It is found that air in the pipe has
a) three nodes and three antinodes
b) three nodes and four antinodes
c) four nodes and three antinodes
d) four nodes and four antinodes.
Answer: d

Question: Two waves of wavelengths 99 cm and 100 cm both travelling with velocity 396 m/s are made to interfere. The number of beats produced by them per second is
a) 1
b) 2
c) 4
d) 8
Answer: c

Question: An organ pipe, open from both end produces 5 beats per second when vibrated with a source of frequency 200 Hz. The second harmonic of the same pipes produces 10 beats per second with a source of frequency 420 Hz. The fundamental frequency of organ pipe is
a) 195 Hz
b) 205 Hz
c) 190 Hz
d) 210 Hz
Answer: b

Question: The length of a sonometer wire AB is 110 cm. Where should the two bridges be placed from A to divide the wire in 3 segments whose fundamental frequencies are in the ratio of 1 : 2 : 3 ?
a) 60 cm and 90 cm
b) 30 cm and 60 cm
c) 30 cm and 90 cm
d) 40 cm and 80 cm
Answer: a

Question: A progressive sound wave of frequency 500 Hz is travelling through air with a speed of 350 ms–1. A compression maximum appears at a place at a given instant. The minimum time interval after which the rarefraction maximum occurs at the same point, is
a) 200 s
b) 1/250s
c) 1/500s
d) 1/1000s
Answer: d

Question: Where should the two bridges be set in a 110cm long wire so that it is divided into three parts and the ratio of the frequencies are 3 : 2 : 1 ?
a) 20cm from one end and 60cm from other end
b) 30cm from one end and 70cm from other end
c) 10cm from one end and 50cm from other end
d) 50cm from one end and 40cm from other end
Answer: a

Question: In a guitar, two strings A and B made of same material are slightly out of tune and produce beats of frequency 6 Hz. When tension in B is slightly decreased, the beat frequency increases to 7 Hz. If the frequency of A is 530 Hz, the original frequency of B will be
a) 523 Hz
b) 524 Hz
c) 536 Hz
d) 537 Hz
Answer: b

Question: When a sound wave of frequency 300 Hz passes through a medium, the maximum displacement of a particle of the medium is 0.1 cm. The maximum velocity of the particle is equal to
a) 60p cms^–1
b) 30p cms^–1
c) 30 cms–1 30 cms^–1
d) 60 cms^–1
Answer: a

Question: A cylindrical tube, open at both ends has fundamental frequency f in air. The tube is dipped vertically in water, so that half of it is in water. The fundamental frequency of air column is now
a) f /2
b) 3f /4
c) 2f
d) f
Answer: d

Question: A standing wave having 3 nodes and 2 antinodes is formed between two atoms having a distance 1.21 Å between them. The wavelength of the standing wave is
a) 6.05 Å
b) 2.42 Å
c) 1.21 Å
d) 3.63 Å
Answer: c

Question: A sound wave is passing through air column in the form of compression and rarefaction. In consecutive compressions and rarefactions,
a) density remains constant
b) Boyle’s law is obeyed
c) bulk modulus of air oscillates
d) there is no transfer of heat
Answer: d

Question: If we study the vibration of a pipe open at both ends, then which of the following statements is not true ?
a) Odd harmonics of the fundamental frequency will be generated
b) All harmonics of the fundamental frequency will be generated
c) Pressure change will be maximum at both ends
d) Antinode will be at open end
Answer: c

Question: For production of beats the two sources must have
a) different frequencies and same amplitude
b) different frequencies
c) different frequencies, same amplitude and same phase
d) different frequencies and same phase
Answer: b

Question: A tuning fork of freqqency 512 Hz makes 4 beats per second with the vibrating string of a piano. The beat frequency decreases to 2 beats per sec when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was
a) 510 Hz
b) 514 Hz
c) 516 Hz
d) 508 Hz
Answer: d

Question: Two waves are represented by the equations y1 = a sin (wt + kx + 0.57) m and y2 = a cos (wt + kx) m, where x is in meter and t in sec. The phase difference between them is
a) 1.0 radian
b) 1.25 radian
c) 1.57 radian
d) 0.57 radian
Answer: a

Question: A source X of unknown frequency produces 8 beats per second with a source of 250 Hz and 12 beats per second with a source of 270 Hz. The frequency of the source X is
a) 242 Hz
b) 258 Hz
c) 282 Hz
d) 262 Hz
Answer: b

Question: A whistle of frequency 1000 Hz is sounded on a car travelling towards a cliff with velocity of 18 m s^–1 normal to the cliff. If c = 330 m s^–1, then the apparent frequency of the echo as heard by the car driver is nearly
a) 1115 Hz
b) 115 Hz
c) 67 Hz
d) 47.2 Hz
Answer: a

Question: An organ pipe P1 closed at one end vibrating in its first overtone and another pipe P2 open at both ends vibrating in third overtone are in resonance with a given tuning fork.The ratio of the length of P1 to that of P2 is
a) 8/3
b) 3/8
c) 1/2
d) 1/3
Answer: b

Question: The number of possible natural oscillation of air column in a pipe closed at one end of length 85 cm whose frequencies lie below 1250 Hz are : (velocity of sound = 340 ms^–1)
a) 4
b) 5
c) 7
d) 6
Answer: d

Question: An engine running at speed /v10 sounds a whistle of frequency 600 Hz. A passenger in a train coming from the opposite side at speed V/15 experiences this whistle to be of frequency f. If v is speed of sound in air and there is no wind, f is near to
a) 710 Hz
b) 630 Hz
c) 580 Hz
d) 510 Hz
Answer: a

Question: Two sources P and Q produce notes of frequency 660 Hz each. A listener moves from P to Q with a speed of 1 ms^–1. If the speed of sound is 330 m/s, then the number of beats heard by the listener per second will be
a) zero
b) 4
c) 8
d) 2
Answer: b

Question: A person carrying a whistle emitting continuously a note of 272 Hz is running towards a reflecting surface with a speed of 18 km h^–1. The speed of sound in air is 345 m s^–1. The number of beats heard by him is
a) 4
b) 6
c) 8
d) zero
Answer: c

Question: With propagation of longitudinal waves through a medium, the quantity transmitted is
a) matter
b) energy
c) energy and matter
d) energy, matter and momentum
Answer: b