# MCQs for Physics Class 11 with Answers Chapter 15 Waves

Students of class 11 Physics should refer to MCQ Questions Class 11 Physics Waves with answers provided here which is an important chapter in Class 11 Physics NCERT textbook. These MCQ for Class 11 Physics with Answers have been prepared based on the latest CBSE and NCERT syllabus and examination guidelines for Class 11 Physics. The following MCQs can help you to practice and get better marks in the upcoming class 11 Physics examination

## Chapter 15 Waves MCQ with Answers Class 11 Physics

MCQ Questions Class 11 Physics Waves provided below have been prepared by expert teachers of grade 11. These objective questions with solutions are expected to come in the upcoming Standard 11 examinations. Learn the below provided MCQ questions to get better marks in examinations.

Question. A travelling wave represented by y (x, t) = asin(kx – ωt) is superimposed on another wave represented by y(x, t) = asin(kx + ωt). The resultant is a

B

Question. At what temperature will the speed of sound in air be 3 times its value at 0°C?
(a) 1184°C
(b) 1148°C
(c) 2184°C
(d) 2148°C

C

Question. The transverse displacement of a string clamped at its both ends is given by y (x, t) = 0.06 sin {2π/3 x} cos(120πt) where x and y are in m and t in s. The length of the string is 1.5 m and its mass is 3 × 10–2 kg. The tension in the string is
(a) 324 N
(b) 648 N
(c) 832 N
(d) 972 N

B

Question. Three travelling waves in same direction are superimposed. The equations of wave are

and the phase difference between resultant wave and first wave is p/4, then f is
(a) π/6
(b) π/3
(c) π/12
(d) none of these

C

Question. For the wave shown in figure, if its position at t = 0, the equation of the wave is
[Speed of wave is v = 300 ms–1]

(a) y = 0.06 sin (23562 t – 78.5 x)
(b) y = 0.06 sin (78.5 x – 23562 t)
(c) y = 0.05 cos (23562 x – 78.5 t)
(d) y = 0.05 sin (78.5 x– 23562 t)

B

Question. For the travelling harmonic wave y(x, t) = 2 cos2π(10t – 0.008x + 0.35) where x and y are in cm and t is in s. The phase difference between oscillatory motion of two points separated by a distance of 0.5 m is
(a) 0.2π
(b) 0.4π
(c) 0.6π
(d) 0.8π

D

Question. A 10 m long steel wire has mass 5 g. If the wire is under a tension of 80 N, the speed of  transverse waves on the wire is
(a) 100 m s–1
(b) 200 m s–1
(c) 400 m s–1
(d) 500 m s–1

C

Question. A body sends waves 100 mm long through medium A and 0.25 m long in medium B. If the  velocity of waves in medium A is 80 cm s–1. The velocity of waves in medium B is
(a) 1 m s–1
(b) 2 m s–1
(c) 3 m s–1
(d) 4 m s–1

B

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

D

Question. A vibrating tuning fork of frequency u is placed near the open end of a long cylindrical tube. The tube has a side opening and is also fitted with a movable reflecting piston. As the piston is moved through 8.75 cm, the intensity of sound changes from a maximum to minimum. If the speed of sound is 350 m s–1, then u is

(a) 500 Hz
(b) 1000 Hz
(c) 2000 Hz
(d) 4000 Hz

B

Question. A man standing between two parallel hills, claps his hand and hears successive echoes at  regular intervals of 1 s. If velocity of sound is 340 m s–1, then the distance between the hills is (Assume that he hears the first echo after 1s
(a) 100 m
(b) 170 m
(c) 510 m
(d) 340 m

C

Question. Two points on a travelling wave having frequency 500 Hz and velocity 300 m/s are 60° out of phase, then the minimum distance between the two points is
(a) 0.2 m
(b) 0.1 m
(c) 0.5 m
(d) 0.4 m

B

Question. A sinusoidal wave travelling in the positive direction has an amplitude of 15 cm, wavelength  40 cm and frequency 8 Hz. The vertical displacement of the medium at t = 0 and x = 0 is also 15 cm (see figure). The phase constant d and expression for wave functions are

C

Question. Equation of a plane progressive wave is given by y = 0.6sin 2π (t – x/2) . On reflection from a denser medium its amplitude becomes (2/3) of the amplitude of the incident wave. The equation of the reflected wave is

B

Question. Sound waves of wavelength λ travelling in a medium with a speed of v enter into another  medium where its speed is 2 v. Wavelength of sound waves in the second medium is
(a) λ
(b) λ/2
(c) 2λ
(d) 4λ

C

Question. A uniform rope of length 10 m and mass 6 kg hangs vertically from a rigid support. A block of mass 2 kg is attached at the lower end. A transverse wave of wavelength 2 cm is created at the lower end A of the rope. What is the wavelength at the end B when the wave reaches the top?

(a) 2 cm
(b) 4 cm
(c) 6 cm
(d) 10 cm

B

Question. From a point source, if amplitude of waves at a distance r is A, its amplitude at a distance 2r will be
(a) A
(b) 2 A
(c) A/2
(d) A/4

C

Question. The displacement of a wave is given by y = 0.001 sin (100t + x) where x and y are in metre and t is in second. This represents a wave
(a) of wavelength one metre
(b) travelling with a velocity of 100 m/s in the negative x-direction
(c) of frequency 100/π Hz
(d) travelling with a velocity of 50/π m/s in the positive x-direction.

B

Question. A bat flying above lake emits ultrasonic sound of 100 kHz. When this wave falls on the water surface, it is partly reflected and partly transmitted. The wavelengths of the reflected and the transmitted waves are (The speed of sound in air is 340 m/s and in water is 1450 m/s)
(a) 6.8 mm and 2.9 mm
(b) 3.4 mm and 1.45 cm
(c) 3.4 mm and 7.8 mm
(d) 6.8 mm and 11.45 cm

B

Question. According to Newton’s formula, the speed of sound in air at STP is
(Take the mass of 1 mole of air is 29 × 10–3 kg)
(a) 250 m s–1
(b) 260 m s–1
(c) 270 m s–1
(d) 280 m s–1

D

Question. A transverse wave is represented by y = Asin(ωt – kx). For what value of the wavelength is the wave velocity equal to the maximum particle velocity?
(a) πA/2
(b) πA
(c) 2πA
(d) A

C

Question. The displacement y (in cm) produced by a simple harmonic progressive wave is

What is the periodic time and maximum velocity of the particles in the medium?
(a) 10–2 sec and 2000 m/s
(b) 10–3 sec and 200 m/s
(c) 10–3 sec and 300 m/s
(d) 10–4 sec and 200 m/s

B

Question. A small speaker delivers 2 W of audio output. At what distance from the speaker will one detect  120 dB intensity sound? [Given reference intensity of sound as 10–12 W/m2]
(a) 30 cm
(b) 10 cm
(c) 40 cm
(d) 20 cm

C

Question. Figure given shows a sinusoidal wave on a string. If the frequency of the wave is 150 Hz,  what is the velocity and wavelength of the given wave?

(a) 0.04 m, 10 m s–1
(b) 0.06 m, 12 m s–1
(c) 0.08 m, 10 m s–1
(d) 0.08 m, 12 m s–1

D

Question. A bat emits ultrasonic sound of frequency 100 kHz in air. If this sound meets a water surface, the wavelengths of the reflected and transmitted sound are (Speed of sound in air = 340 m s–1 and in water = 1500 m s–1)
(a) 3.4 mm, 30 mm
(b) 6.8 mm, 15 mm
(c) 3.4 mm, 15 mm
(d) 6.8 mm, 30 mm

C

Question. A string of mass 2.5 kg is under a tension of 200 N. The length of the stretched string is 20 m. If the transverse jerk is struck at one end of the string, the disturbance will reach the other end in
(a) one second
(b) 0.5 second
(c) 2 second
(d) data given is insufficient

B

Question. A sound wave travels with a velocity of 300 m s–1 through a gas. 9 beats are produced in 3s when two waves pass through it simultaneously. If one of the waves has 2 m wavelength, the waveleng -th of the other wave is
(a) 1.98 m
(b) 2.04 m
(c) 3.15 m
(d) 0.99 m

B

Assertion & Reasoning Based MCQs :

two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

Question. Assertion (A) : The velocity of sound increases with increases in humidity.
Reason (R) : Velocity of sound does not depends upon the medium.

C

Question. Assertion (A) : In a stationary wave, there is no transfer of energy.
Reason (R) : There is no onward motion of the disturbance from one particle to adjoining particle in stationary wave.

B

Question. Assertion (A) : A vibrating tuning fork sounds louder when its stem is pressed against a desk top.
Reason (R) : When a wave reaches another denser medium, part of the wave is reflected.

C

Question. Assertion (A) : Under given conditions of pressure and temperature, sound travels faster in a monatomic gas than in diatomic gas.
Reason (R) : Opposition for wave to travel is more in diatomic gas than monatomic gas.

C

Question. Assertion (A) : Two arms of a tuning fork vibrate in different phase.
Reason (R) : Each arm has the same frequency of vibration.

B

Question. Assertion (A) : Longitudinal waves travel through air in an organ pipe.
Reason (R) : Air possesses only volume elasticity.

A

Question. Assertion (A) : Particle velocity depends on time.
Reason (R) : For the propagation of wave motion, the medium must have the properties of elasticity and inertia.

B

Case Based MCQs :

Beat
The phenomenon of regular variation in intensity of sound with time at a particular position due to superposition of two sound waves of slightly different frequencies is called beats.
For waves

Question. Two turning forks of frequencies n1 and n2 produces n beats per second. If n2 and n are  known, n1 may be given by

C

Question. P and Q are two wires whose fundamental frequencies are 256 Hz and 382 Hz respectively. How many beats in two seconds will be heard by the third harmonic of A and second harmonic of B?
(a) 4
(b) 8
(c) 16
(d) zero

B

Question. Which of the following phenomenon is used by the musicians to tune their musical  instruments?
(a) Interference
(b) Diffraction
(c) Beats
(d) Polarisation

C

Question. The phenomenon of beats can take place
(a) for longitudinal waves only
(b) for transverse wave only
(c) for sound waves only
(d) for both longitudinal and transverse waves

D

Question. When two waves of almost equal frequencies v1 and v2 reach at a point simultaneously, the  time interval between successive maxima is

D

Transverse and Longitudinal Waves
Transverse waves forms if the particles of the medium vibrate at right angle to the direction of wave motion energy propagation, the wave is called transverse wave. These are propagated as crests and troughs.

Longitudinal waves forms if the particles of the medium vibrate in the direction of wave motion, the wave is called longitudinal. These are propagated as compressions and rarefactions and wave is also known as pressure or compressional wave. Wave on spring or sound waves in air are examples of longitudinal waves.

Question. Sound waves travel fastest in
(a) solids
(b) liquids
(c) gases
(d) vacuum

A

Question. A transverse wave consists of
(a) only crests
(b) only troughs
(c) both crests and troughs
(d) rarefactions and compressions

C

Question. In a transverse wave, the particles of the medium
(a) vibrate in a direction perpendicular to the direction of the propagation
(b) vibrate in a direction parallel to the direction of the propagation
(c) move in circle (d) move in ellipse.

A

Question. Sound waves in air cannot be polarized because
(a) their speed is small
(b) they require medium
(c) they are longitudinal
(d) their speed is temperature dependent

C

Question. Ultrasonic waves produced by a vibrating quartz crystal are
(a) only longitudinal
(b) only transverse
(c) both longitudinal and transverse
(d) neither longitudinal nor transverse