Tag: beats in sound waves

Questions Related to beats in sound waves

What happens when two sound waves of frequencies differing by more than 10 Hz reach our ear simultaneously?

physics beats in sound waves

  1. beats are not produced

  2. the waves destroy each other's effect

  3. interference of sound does not take place.

  4. beats are produced but cannot be heard

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Correct Option: D
Explanation:

 if the beat formation rate is too fast (more than 10 Hz) human ear could not distinguish the time interval of the two consicutive beats. 

You are listening to an $A$ note played on a violin string. Let the subscript $s$ refer to the violin string and $a$ refer to the air. Then:

physics beats in sound waves

  1. $f _{s}=f _{a}$ but $\lambda _{s}\neq\lambda _{a}$

  2. $f _{s}=f _{a}$ and $\lambda _{s}=\lambda _{a}$

  3. $\lambda _{s}=\lambda _{a}$ but $f _{s}\neq f _{a}$

  4. $\lambda _{s}\neq\lambda _{a}$ and $f _{s}\neq f _{a}$

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Correct Option: A
Explanation:

Frequencies of air and string is same because the source is same. Air and the string are two different medium so there velocities will also different. Hence the wavelength has to be different.

The fundamental frequency of a sitar wire is 440 vibrations per seond. If the sitar player reduces the length of the wire by $1/5^{th}$, then the change in the frequency of sitater wire will be

physics beats in sound waves

  1. 2200 vibrations/sec

  2. 1760 vibrations/sec

  3. 440 vibrations/sec

  4. 110 vibrations/sec

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Correct Option: A

When a long hollow cylindrical iron pipe is struck at one end, then at the other end of the pipe :

physics beats in sound waves

  1. one sound is only heard

  2. two sounds are heard at different intervals

  3. three sounds are heard at different intervals

  4. no sound is heard

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Correct Option: B
Explanation:

There will be two sounds, one will through the air , and other will come through the material, Sound speed is faster in steel, therefore it will be heard earlier than the sound from air . Option "B" is correct.

The following is best Lubricant?

physics beats in sound waves

  1. Solids

  2. Liquid

  3. Gas

  4. Both B and c

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Correct Option: B

A source of sound of frequency 256 Hz is moving towards a wall with a velocity of 5 m/s. The number of beats per second heard by a stationary observer between the source and the wall is (Velocity of sound = 330 m/s) 

physics beats in sound waves

  1. 8

  2. 3

  3. 5

  4. 2

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Correct Option: A
Explanation:
 If the sound reaches the observer after being reflected from a stationary surface and the medium is also stationary$,$ 
the image of the source in the reflecting surface will become the source of the reflected sound$.$
$v = v [c – v-o/c – v _s]$
$v _o,$ $v _s$ are $+ve$ if they are directed from source to the observer and $– ve$ if they directed from observer to source$.$
$v = 256 [330 – (- 5)/330 – 5] = 264 Hz$
$∴$ Beat frequency $= 264 – 256 = 8$
Hence,
option $(A)$ is correct answer.

Megaphones or loudhailers, horns, musical instruments such as trumpets and shehanais, are all designed to---------

physics beats in sound waves

  1. send sound in a particular direction without spreading it in all directions

  2. send sound in a particular direction spreading it in all directions

  3. collect sound from all directions spreading it in all directions

  4. all

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Correct Option: A
Explanation:

Megaphones or loudhailers, horns, musical instruments such as trumpets and  shehanais, are all designed to send sound in a particular direction without spreading it in all direction. In these instruments, a tube followed by a conical opening reflects sound successively to guide most of the sound waves from the source in the forward direction towards the audience.

Two waves $\mathrm{y} _{1}=\mathrm{A}\cos(0.5\pi \mathrm{x}-100\pi \mathrm{t})$
and $\mathrm{y} _{2}=\mathrm{A}\cos(0.46\pi \mathrm{x}-92\pi \mathrm{t})$ are travelling in a pipe placed along $\mathrm{x}$-axis. Find the number of times intensity is maximum in time interval of 1 sec.

physics beats in sound waves

  1. 4

  2. 6

  3. 8

  4. 10

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Correct Option: A
Explanation:

Beat frequency$=|f _1-f _2|=(50-46)=4s^{-1}$

One beat frequency consists of a maximum and a minimum
So the number of maxima are ${f}=4$

The lowest wavelength of audible sound is (Velocity of sound in air is $340ms^{-1}$)

physics beats in sound waves

  1. $1.7cm$

  2. $17m$

  3. $20cm$

  4. $20000m$

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Correct Option: B

The maximum time period for a sound wave that the audible to normal human being is

physics beats in sound waves

  1. $0.5s$

  2. $5s$

  3. $0.05s$

  4. $0.005s$

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Correct Option: C