Tag: physics

Questions Related to physics

A body is walking away from a wall towards an observe at a speed of 1 m/s and blows a whistle whose frequency is 680 Hz. The number of beats heard by the observe per second is approximately.(velocity of sound in air = 340 m/s)

physics superposition of waves-1: interference and beats distinction between interference and beats beats and its applications beats in sound waves

  1. 4

  2. 8

  3. 2

  4. zero

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Correct Option: A

Two sound waves of equal intensity I produce beats . The maximum intensity of sound produced in beats will be

physics superposition of waves-1: interference and beats distinction between interference and beats beats and its applications beats in sound waves

  1. I

  2. 4I

  3. 2I

  4. I/2

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Correct Option: C

$y _1 = A cos (2f _1t)$     and $y _2 = A cos (2 f _2t),$, then $y _{total} $ is

physics superposition of waves-1: interference and beats distinction between interference and beats beats and its applications beats in sound waves

  1. $y _{total} = y _1 + y _2 = A {cos (2 f _1t) + cos (2 f _2t)}$

  2. $y _{total} = y _1 - y _2 = A {cos (2 f _1t) - cos (2 f _2t)}$

  3. $y _{total} =\dfrac{ y _1}{ y _2} = A\dfrac{{cos (2 f _1t)}}{{cos (2 f _2t)}}$

  4. $y _{total} = y _1 \times y _2 = A {cos (2 f _1t) \times cos (2 f _2t)}$

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Correct Option: A
Explanation:

Resultant  $(y _{total})$ of the two waves is equal to the superposition of the waves and is given by,
$y _{total}  = y _1+y _2$
$\therefore$  $y _{total} = A \ cos(2f _1t)+ A \ cos(2f _2t)$

A tuning fork of frequency 240 Hz produce 5 beats with a sonometer wire. On increasing the tension in the wire if the number of beats changes to 4 per second, the initial frequency of the wire is

physics superposition of waves-1: interference and beats distinction between interference and beats beats and its applications beats in sound waves

  1. 8285 Hz

  2. 275 Hz

  3. 376 Hz

  4. 264 Hz

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Correct Option: A

Two waves of wavelengths 99 cm and 100 cm both travelling with velocity 396 m/s are made of interfere. The number of beats produced by them per second are

physics superposition of waves-1: interference and beats distinction between interference and beats beats and its applications beats in sound waves

  1. $1$

  2. $2$

  3. $4$

  4. $8$

Show answer
Correct Option: C
Explanation:

$\begin{array}{l} Velocity\, \, of\, \, wave\, \, V=n\lambda  \ Where\, \, n=frequency\, \, of\, \, wave\, \,  \ \Rightarrow n=\frac { v }{ \lambda  }  \ { n _{ 2 } }=\frac { { { v _{ 2 } } } }{ { { \lambda _{ 2 } } } } =\frac { { 396 } }{ { 100\times { { 10 }^{ -2 } } } } =396Hz \ no.\, \, of\, \, beats\, \, ={ n _{ 1 } }-n _2\, =4 \end{array}$

If 2 waves of same frequency and same amplitude on superposition, produce a resultant disturbance of the same amplitude, the waves differ in phase by

physics superposition of waves-1: interference and beats distinction between interference and beats beats and its applications beats in sound waves

  1. $ \dfrac { \pi }{ 3 } $

  2. $ \dfrac { 2\pi }{ 3 } $

  3. $ { \pi } $

  4. $ { 3\pi } $

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Correct Option: B
Explanation:

Let the amplitude of each wave be $A$ i.e.  $A _1 = A _2 = A$
Thus amplitude of resultant wave  $A _R =A$
Using   $A^2 _R =  A _1^2 + A _2^2 + 2A _1A _2 \cos\theta$
$\therefore$  $A^2 =  A^2 + A^2 + 2A^2 \cos\theta$
Or  $\cos\theta = -0.5$
$\implies  \ \theta = \dfrac{2\pi}{3}$

Two identical wires are stretched by the same tension of $101$ N & each emits a note of frequency $202$ Hz. If the tension in one wire is increased by $1N$ , then the beat frequency is:

physics superposition of waves-1: interference and beats distinction between interference and beats beats and its applications beats in sound waves

  1. $2 Hz$

  2. $\frac{1}{2}Hz$

  3. $1 Hz$

  4. None of these

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Correct Option: C

Which of the following is associated with liquid only and not for the gases?

intermolecular forces: cohesive and adhesive forces surface tension properties of matter physics

  1. Pressure

  2. Volume

  3. Density

  4. Surface tension

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Correct Option: D
Explanation:

Surface tension is the energy possessed by the free surface of liquids, and it is concerned with only liquid as gases do not have free surfaces.

The property of fluid which enables it to resist tensile stress is known as 

intermolecular forces: cohesive and adhesive forces surface tension properties of matter physics

  1. compressibility

  2. surface tension

  3. cohesion

  4. adhesion

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Correct Option: B
Explanation:

Surface tension is the property of a fluid which enables it to resist tensile stress.

Surface tension, $S=\dfrac{F}{l}$
It is measured in Newton.

A wire 10  cm long is placed horizontally on the surface of water. It is gently pulled up with a force of $1.4 \times 10^{-2}$ N to keep it in equilibrium. The surface tension of water is

intermolecular forces: cohesive and adhesive forces surface tension properties of matter physics

  1. 50 dyne /cm

  2. 60 dyne/cm

  3. 70 dyne/cm

  4. 40 dyne/cm

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Correct Option: A