Waves — DPP 2

20 NEET questions from Waves, with answers and explanations. Attempt it as a timed test to get scoring, accuracy breakdown and mistake tracking.

Attempt this test free 20 questions · 30 minutes · +80 marks
1
The speed of sound in gas of density ρ at a pressure P is proportional
  1. A $\left( \frac { \mathrm { P } } { \rho } \right) ^ { 2 }$
  2. B $\left( \frac { \mathrm { P } } { \rho } \right) ^ { 3 / 2 }$
  3. C $\sqrt { \frac { \rho } { \mathrm { P } } }$
  4. D $\sqrt { \frac { \mathrm { P } } { \rho } }$
Show answer

Correct answer: D

2
A wave represented by the equation $y = \operatorname { acos } ( k x - \omega t )$ is superposed with another wave to form a stationary wave such that point x = 0 is a node. The equation for the other wave is:
  1. A $a \cos ( k x - \omega t )$
  2. B $- a \cos ( k x - \omega t )$
  3. C $- a \cos ( k x + \omega t )$
  4. D $- a \sin ( k x - \omega t )$
Show answer & explanation

Correct answer: C

Node at x = 0, (Destructive Interference)
At these points ϕ = (2n – 1)π, i.e., an odd multiple of π.
$\therefore Y_{1}=a \cos (k x-\omega t) \quad Y_{2}=-a \cos (k x+\omega t)$
Therefore, option (C) is the correct answer.
3
In a stretched string.
  1. A Only transverse waves can exist
  2. B Only longitudinal waves can exist
  3. C Both transverse and longitudinal waves can exist
  4. D None of these
Show answer

Correct answer: A

4
Motion of two particles is given by: $y _ { 1 } = 0.25 \sin ( 310 t )$, $y _ { 2 } = 0.25 \sin ( 316 t )$ find beat frequency:
  1. A 3
  2. B 3/π
  3. C 6/π
  4. D 6
Show answer & explanation

Correct answer: B

$\begin{array}{l}y_{1}=0.25 \sin (310 t), y_{2}=0.25 \sin (316 t) \\ \omega_{1}=310, f_{1}=\frac{310}{2 \pi} \\ \omega_{2}=316, f_{2}=\frac{316}{2 \pi} \\ \text { Number of beats }=f_{2}-f_{1}=\frac{316}{2 \pi}-\frac{310}{2 \pi}=\frac{3}{\pi}\end{array}$
Therefore, option (B) is the correct answer.
5
The phenomenon of sound propagation in air is
  1. A An isothermal process
  2. B An adiabatic process
  3. C An isobaric process
  4. D An isochoric process
Show answer

Correct answer: B

6
A wave travelling in the + ve x-direction having displacement of particle along y-direction as 1 m, wavelength 2π m, and frequency of 1/π Hz is represented by:
  1. A $y = \sin ( 2 \pi x + 2 \pi t )$
  2. B $y = \sin ( x - 2 t )$
  3. C $y = \sin ( 2 \pi x - 2 \pi t )$
  4. D $y = \sin ( 10 \pi x - 20 \pi t )$
Show answer

Correct answer: B

7
Three sound waves of equal amplitudes have frequencies (v - 1), v, (v + 1). They superpose to give beats. The number of beats produced per second will be:
  1. A v
  2. B v/2
  3. C 2
  4. D 1
Show answer & explanation

Correct answer: C

Beats = f$_{3}$ – f$_{1}$ = (ν + 1) – (ν – 1) = 2
Therefore, option (C) is the correct answer.
8
A point source emits sound equally in all directions in a nonabsorbing medium. Two points P and Q are at distance of 2 m and 3 m respectively from the source. The ratio of the intensities of the waves at P and Q is:
  1. A 9 : 4
  2. B 2 : 3
  3. C 3 : 2
  4. D 4 : 9
Show answer & explanation

Correct answer: A

$I \propto \frac{1}{d^{2}}$
$\therefore \frac{I_{1}}{I_{2}}=\frac{d_{2}^{2}}{d_{1}^{2}}=\frac{(3)^{2}}{2^{2}}=\frac{9}{4}$
Therefore, option (A) is the correct answer.
9
For a standing wave, $y = 10 \sin \left( \frac { \pi } { 18 } x \right) \cos ( 84 \pi t ) m$, the distance (in metre) between a node and the next antinode is
  1. A 8.5
  2. B 9.0
  3. C 18
  4. D 19
Show answer

Correct answer: B

10
A wave is represented by the equation
$y = A \sin 314 \left[ \frac { t } { 0.5 s } - \frac { x } { 100 m } \right]$
The frequency is n, and the wavelength is λ:
  1. A n = 2 Hz, λ = 2 m
  2. B n = 2 Hz, λ = 100 m
  3. C n = 100 Hz, λ = 2 m
  4. D n = 100 Hz, λ = 100 m
Show answer & explanation

Correct answer: C

Waves – NEET-18752
11
Assertion (A): The pitch of female voice is higher than the pitch of male voice.
Reason (R): Pitch distinguishes between a shrill and a grave sound.
  1. A Both Assertion (A) and Reason are True and the Reason (R) is a correct explanation of the Assertion (A).
  2. B Both Assertion (A) and Reason (R) are True but Reason (R) is not a correct explanation of the Assertion (A).
  3. C Assertion (A) is True but the Reason (R) is False
  4. D Assertion (A) and Reason (R) are False
Show answer

Correct answer: B

12
Two pulses in a stretched string whose centres are initially 8 cm apart are moving towards each other as shown in the figure. The speed of each pulse is 2 cm/s. After 2 seconds, the total energy of the pulses will be:
Waves – NEET-18761
  1. A Zero
  2. B Purely kinetic
  3. C Purely potential
  4. D Purely kinetic and partly potential.
Show answer & explanation

Correct answer: A

Zero. Energy would be present in both, but as the waves are in opposite directions. Thus, cancels out. Therefore, option (A) is the correct answer.
13
An observer standing on the sea coast finds that 54 ripples reach the surface per minute. If the wavelength of the ripples is 10 m, what is the wave velocity?
  1. A 54 m/s
  2. B 9 m/s
  3. C 10 m/s
  4. D 6 m/s
Show answer & explanation

Correct answer: B

Frequency $=\frac{54}{60}$ and $c=f \lambda=\frac{54}{60} \times 10=9 \mathrm{~m} / \mathrm{s}$
Therefore, option (B) is the correct answer.
14
Which of the following phenomenon cannot take place with sound waves?
  1. A Polarisation
  2. B Refraction
  3. C Diffraction
  4. D Reflection
Show answer

Correct answer: A

15
When a wave propagating through a medium encounters a change in medium, then which of the following property remains same?
  1. A Speed
  2. B Amplitude
  3. C Frequency
  4. D Wavelength
Show answer

Correct answer: C

16
A transverse wave travels along the x-axis. The particles of medium move
  1. A Along x-axis
  2. B Along y-axis
  3. C Along z-axis
  4. D Either along y-axis or z-axis
Show answer

Correct answer: D

17
The speed of sound in air is independent from its
  1. A Amplitude
  2. B Frequency
  3. C Phase
  4. D All of these
Show answer

Correct answer: D

18
Equation of a plane progressive wave is given by $y = 0.6 \mathrm { sin } 2 \pi \left( \mathrm { t } - \frac { \mathrm { x } } { 2 } \right)$. On reflection from a denser medium its amplitude becomes $\frac { 2 } { 3 }$ of the amplitude of the incident wave. The equation of the reflected wave is:
  1. A $\mathrm { y } = 0.6 \sin 2 \pi \left( \mathrm { t } + \frac { \mathrm { x } } { 2 } \right)$
  2. B $\mathrm { y } = - 0.4 \sin 2 \pi \left( \mathrm { t } + \frac { \mathrm { x } } { 2 } \right)$
  3. C $y = 0.4 \sin 2 \pi \left( t + \frac { x } { 2 } \right)$
  4. D $\mathrm { y } = - 0.4 \sin 2 \pi \left( \mathrm { t } - \frac { \mathrm { x } } { 2 } \right)$
Show answer & explanation

Correct answer: D

Waves – NEET-18759
19
A second harmonic has to be generated in a string of length L stretched between two rigid supports. The points where the string has to be plucked and touched are:
  1. A Plucked at $\frac { \mathrm { L } } { 4 }$ and touch at $\frac { \mathrm { L } } { 2 }$
  2. B Plucked at $\frac { \mathrm { L } } { 4 }$ and touch at $\frac { 3 \mathrm {~L} } { 2 }$
  3. C Plucked at $\frac { \mathrm { L } } { 2 }$ and touch at $\frac { \mathrm { L } } { 2 }$
  4. D Plucked at $\frac { \mathrm { L } } { 2 }$ and touch at $\frac { 3 \mathrm {~L} } { 4 }$
Show answer & explanation

Correct answer: A

Waves – NEET-18760 Plucked at $\frac{L}{4}$ and $\frac{3 L}{4}$
Touched at $\frac{L}{2}$ and L
Therefore, option (A) is the correct answer.
20
A tuning fork having frequency 300 Hz produce, four beat per sec with x. If we file arm of unknown and again vibrate, number of beats decreases determine x.
  1. A 296 Hz
  2. B 304 Hz
  3. C Both (A) and (B)
  4. D 300 Hz
Show answer

Correct answer: A

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