CBSE Class 11 Waves Worksheet B

Question. The speed of sound in air under ordinary conditions is around 330 m s^–1. The speed of sound in hydrogen under similar conditions will be (in m s–1) nearest to
(a) 330
(b) 1200
(c) 600
(d) 900

Answer: B

Question. The equation of a progressive wave is y = 0.02sin 2π [t/0.01 - x/0.30] Here x and y are in metre and t is in second. The velocity of propagation of the wave is
(a) 300 m s^–1
(b) 30 m s^–1
(c) 400 m s^–1
(d) 40 m s^–1

Answer: B

Question. A pipe closed at one end produces a fundamental note of 412 Hz. It is cut into two pieces of equal length. the fundamental frequencies produced by the two pieces are
(a) 206 Hz, 412 Hz
(b) 824 Hz, 1648 Hz
(c) 412 Hz, 824 Hz
(d) 206 Hz, 824 Hz

Answer: B

Question. A train has just completed U-curve in a track which is a semicircle. The engine is at the forward end of the semi-circular part of the track while the last carriage is at the rear end of the semi circular track. The driver blows a whistle of frequency 200 Hz. Velocity of sound is 340 m/sec Then the apparent frequency as observed by a passenger in the middle of the train, when the speed of the train is 30 m/sec is
(a) 181 Hz
(b) 200 Hz
(c) 188 Hz
(d) 210 Hz

Answer: B

Question. The displacement of a particle varies according to the relation x = 4(cos πt + sin πt). The amplitude of the particle is
(a) – 4 m
(b) 4 m
(c) 4 √2m
(d) 8 m

Answer: C

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 engine running at speed v/10 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. A source of sound produces waves of wavelength 60 cm when it is stationary. If the speed of sound in air is 320 m s^–1 and source moves with speed 20 m s^–1, the wavelength of sound in the forward direction will be nearest to
(a) 56 cm
(b) 60 cm
(c) 64 cm
(d) 68 cm

Answer: A

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. The equation Y = 0.02 sin (500pt) cos (4.5 x) represents
(a) progressive wave of frequency 250 Hz along x-axis
(b) a stationary wave of wavelength 1.4 m
(c) a transverse progressive wave of amplitude 0.02 m
(d) progressive wave of speed of about 350 m s–1

Answer: B

Question. If the speed of a transverse wave on a stretched string of length 1 m is 60 m/s, what is the fundamental frequency of vibration?
(a) 10 Hz
(b) 30 Hz
(c) 40 Hz
(d) 70 Hz

Answer: B

Question. Wave pulse on a string shown in figure is moving to the right without changing shape. Consider two particles at positions x1 = 1.5m and x2 = 2.5m. Their transverse velocities at the moment shown in figure are along directions 

(a) positive y-axis and positive y-axis respectively
(b) negative y-axis and positive y-axis respectively
(c) positive y-axis and negative y-axis respectively
(d) negative y-axis and negative y-axis respectively

Answer: B

Question. The transverse wave represented by the equation y = 4 sin(π/6) sin (3x - 15t) has
(a) amplitude = 4
(b) wavelength = 4 π/3
(c) speed of propagation = 5
(d) period = π/15

Answer: C

Question. A longitudinal wave is represented by x = x₀ sin 2π(nt - x/λ) The maximum particle velocity will be four times the wave velocity if 

Answer: C

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 v_B. The ratio v_A / v_B is
(a) 1/2
(b) 2
(c) 1/4
(d) 4

Answer: A

Question. A sonometer wire of length l vibrates in fundamental mode when excited by a tuning fork of frequency 416 Hz. If the length is doubled keeping other things same, the string will
(a) vibrate with a frequency of 416 Hz
(b) vibrate with a frequency of 208 Hz
(c) vibrate with a frequency of 832 Hz
(d) stop vibrating

Answer: A

Question. A source of sound is travelling at 100/3 m s^–1 along a road, towards a point A. When the source is 3 m away from A, a person standing at a point O on a road perpendicular to the track hears a sound of frequency n'. The distance of O from A at that time is 4 m. If the original frequency is 640 Hz, then the value of n' is (given : velocity of sound = 340 m s^–1) 

(a) 620 Hz 
(b) 680 Hz
(c) 720 Hz
(d) 840 Hz 

Answer: B

Question. The equation of a stationary wave is : y = 4sin(πx/15) cos(96πt) . The distance between a node and its next antinode is
(a) 7.5 units
(b) 1.5 units
(c) 22.5 units
(d) 30 units

Answer: A

Question. A wave travelling along the x-axis is described by the equation y(x, t) = 0.005 cos (αx – βt). If the wavelength and the time period of the wave are 0.08 m and 2.0s, respectively, then α and β in appropriate units are 

Answer: A

Question. A car is moving towards a high cliff. The car driver sounds a horn of frequency f. The reflected sound heard by the driver has as frequency 2f. If v be the velocity of sound, then the velocity of the car, in the same velocity units, will be
(a) v /2
(b) v /√2
(c) v /3
(d) v /4

Answer: C
 

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1. Velocity of sound increases on a cloudy day. Why?

2. Sound of maximum intensity is heard successively at an interval of 0.2 second on sounding two tuning fork to gather. What is the difference of frequencies of two tuning forks?

3. If two sound waves has a phase difference of 600, then find out the path difference between the two waves?

4. If string wires of same material of length l and 2l vibrate with frequencies 100HZ and 150 HZ. Find the ratio of their frequencies?

5. Two similar sonometer wires of the same material produces 2 beats per second.

The length of one is 50cm and that of the other is 50.1 cm. Calculate the frequencies of two wives?            

6. Why are all stringed instruments provided with hollow boxes?

7. Two waves have equations:- X₁=a Sin (wt + Φ₁) X₂= a Sin (wt + Φ₂)

If in the resultant wave, the amplitude remains equal to the amplitude of the super posing waves. Calculate the phase difference between X₁ and X₂?

8. A Tuning fork of frequency 300HZ resonates with an air column closed at one end at 27°C. How many beats will be heard in the vibration of the fork and the air column at 0°C?

9. A vehicle with horn of frequency ‘n’ is moving with a velocity of 30m|s in a direction perpendicular to the straight line joining the observer and the vehicle. If the observer perceives the sound to have a frequency of n+n₁. Calculate n₁?

10. We cannot hear echo in a room. Explain?

11. Show that the frequency of nth harmonic mode in a vibrating string which is closed at both the end is ‘n’ times the frequency of the first harmonic mode?

Click on link below to download CBSE Class 11 Waves Worksheet B.