Tag: beats in sound waves

Questions Related to beats in sound waves

Two sound sources (of same frequency ) are placed at distance of 100 meter. An observer, when moving between both sources, hears 44 beats per second. The distance between sound source is now changed to 400 meter then the beats/second heard by observer will be  :

  1. 2

  2. 4

  3. 8

  4. 16


Correct Option: D

Two open organ pipes 80 and 81 cm long found to give 26 beats in 10 sec, when each is sounding its fundamental note. Then the velocity of sound in air is

  1. 337 $m s ^ { - 1 }$

  2. 370 $m s ^ { - 1 }$

  3. 345 $m s ^ { - 1 }$

  4. 350 $m s ^ { - 1 }$


Correct Option: A

Two monochromatic light waves of amplitudes $A$ and $2A$ interfering at a point, have a phase difference of ${60^0}.$ The intensity at that point will be  proportional to :

  1. $3{A^2}$

  2. $5{A^2}$

  3. $7{A^2}$

  4. $9{A^2}$


Correct Option: C

Two sound waves with wavelength $5$m and $5.5$ m respectively. each propoggate in a gas with velocity $300$ m/s. we expect the following number of beats per second

  1. 12

  2. 0

  3. 1

  4. 6


Correct Option: D

Two waves are approaching each other with a velocity of $16\, m/s$ and frequency $n$. the distance between two consecutive nodes is 

  1. $\dfrac{16}{n}$

  2. $\dfrac{8}{n}$

  3. $\dfrac{n}{16}$

  4. $\dfrac{n}{8}$


Correct Option: A

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)

  1. 4

  2. 8

  3. 2

  4. zero


Correct Option: A

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

  1. I

  2. 4I

  3. 2I

  4. I/2


Correct Option: C

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

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


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

  1. 8285 Hz

  2. 275 Hz

  3. 376 Hz

  4. 264 Hz


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

  1. $1$

  2. $2$

  3. $4$

  4. $8$


Correct Option: C
Explanation:

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