CLASS : XITH SUBJECT : PHYSICS

DATE : DPP NO. :5

Topic :- WAVES

1. How many times more intense is a 60 dB sound than a dB sound?

a) 1000 b) 2 c) 100 d) 4

2. If the phase difference between two sound waves of wavelength 𝜆 is 60o , the corresponding
path difference is
𝜆 𝜆 𝜆
a) 6 b) 2 c) 2𝜆 d) 4

𝑡 𝑥
3. The equation of progressive wave is𝑦 = 0.2 sin 2𝜋 [ − 0.3], where x and y are in metre and t
0.01
is in second. The velocity of propagation of the wave is
a) 30 ms−1 b) 40 ms−1 c) 300 ms −1 d) 400 ms−1

4. The velocity of sound hydrogen is 1224ms−1. Its velocity in mixture of hydrogen and oxygen
containing 4 parts by volume of hydrogen and 1 part oxygen is
a) 1224ms−1 b) 612ms−1 c) 2448ms−1 d) 306ms−1

5. Two adjacent piano keys are struck simultaneously. The notes emitted by them have
frequencies 𝑛1 and 𝑛2 . The number of beats heard per second is
1 1
a) 2 (𝑛1 − 𝑛2 ) b) (𝑛1 + 𝑛2 )
2
c) 𝑛1 ~𝑛2 d) 2(𝑛1 − 𝑛2 )

6. Two sound waves with wavelengths 5.0 𝑚 and 5.5 𝑚 respectively, each propagate in a gas with
velocity 330 𝑚/𝑠 We expect the following number of beats per second
a) 1 b) 6 c) 12 d) 0

7. A progressive wave y=a sin [(kx-ωt)] is reflected by a rigid wall at x=0. Then the reflected wave
can be represented by
a) y=a sin (kx+ωt) b) y=a cos (kx+ωt) c) y=-a sin (kx-ωt) d) y=-a sin (kx+ωt)

8. Mechanical waves on the surface of a liquid are

a) Transverse b) Longitudinal
c) Torsional d) Both transverse and longitudinal

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 9. It is possible to hear beats from the two vibrating sources of frequency
a) 100 𝐻𝑧 and 150 𝐻𝑧 b) 20 𝐻𝑧 and 25 𝐻𝑧
c) 400 𝐻𝑧 and 500 𝐻𝑧 d) 1000 𝐻𝑧 and 1500 𝐻𝑧

10. If v is the speed of sound in air then the shortest length of the closed pipe which resonates to a
frequency v, is
𝑣 𝑣 4𝑣 2𝑣
a) 2𝑣 b) 4𝑣 c)
𝑣
d)
𝑣

11. Radar waves are sent towards a moving aeroplane and the reflected wave are received. When
the aeroplane is moving towards the radar, the wavelength of the wave
a) Decreases
b) Increases
c) Remains the same
d) Sometimes increases or decreases

12. The vibrating of four air columns are represented in the figure. The ratio of frequencies
𝑛𝑝 : 𝑛𝑞 : 𝑛𝑟 : 𝑛𝑠 is

a) 12:6:3:5 b) 1:2:4:3 c) 4:2:3:1 d) 6:2:3:4

13. If wave 𝑦 = 𝑎 cos(𝜔𝑡 + 𝑘𝑥) is moving along x-axis, the shape of pulse at t=0 and t=2s
a) Are different b) Are same c) May not be same d) None of these

2𝜋
14. The equation of a wave is given by y=10 sin ( 𝑡 + 𝑎). If the displacement is 5 cm at t=0, then
45
the total phase at t=7.5s is
𝜋 𝜋 𝜋
a) 𝜋 b) 6 c) 2 d) 3

15. A micro-wave and an ultrasonic sound wave have the same wavelength. Their frequencies are
in the ratio (approximately)
a) 106 ∶ 1 b) 104 ∶ 1 c) 102 ∶ 1 d) 10 ∶ 1

16. A stationary source is emitted sound at a fixed frequency𝑓0, which is reflected by two cars
approaching the source. The difference between the is frequencies of sound reflected from the
car is 1.2% of 𝑓0. What is the difference in the speed of the cars (in km per hour) to the nearest
integer? The cars are moving at constant speeds much smaller than the speed of sound which is
330𝑚𝑠 −1
a) 7.128 km/h b) 7 km/h c) 8.128 km/h d) 9 km/h

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 17. A travelling wave represented by 𝑦 = 𝑎 sin(𝜔𝑡 − 𝑘𝑥) is superimposed on another wave
represented b𝑦 = 𝑎 sin(𝜔𝑡 + 𝑘𝑥). The resultant is
1 𝜆
a) A standing wave having nodes at 𝑥 = (𝑛 + 2) , 𝑛 = 0,1,2
2
b) A wave travelling along + x direction
c) A wave travelling along - x direction
𝑛𝜆
d) A standing wave having nodes at 𝑥 = ;𝑛 = 0,1,2
2

18. Consider ten identical sources of sound all giving the same frequency but having phase angles
which are random. If the average intensity of each source is 𝐼0 , the average of resultant
intensity 𝐼 due to all these ten sources will be
a) 𝐼 = 100𝐼0 b) 𝐼 = 10𝐼0 c) 𝐼 = 𝐼0 d) 𝐼 = √10𝐼0

19. When both the listener and source are moving towards each other, then which of the following
is true regarding frequency and wavelength of wave observed by the observer?
a) More frequency, less wavelength
b) More frequency, more wavelength
c) Less frequency, less wavelength
d) More frequency, constant wavelength

20. If you set up the seven overtone on a string fixed at both ends, how many nodes and antinodes
are set up in it?
a) 6,5 b) 5,4 c) 4,3 d) 3,2

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