Question

If there are three sources of sound of equal intensity with frequencies 300, 301 and 302, the number of beats heard per second will be:

Solution

Correct option is

1

 

  

        

        

The resultant displacement y is given by,

             

              

                

              

The resultant has the mean frequency 301 Hz and an amplitude A        = a[2 cos 2πt + 1]        

For maximum A, cos 2πt = 1  

  

i.e., the maxima occurs every one sec.

For minimum A (= 0). 

          

i.e., the minima also occurs every one sec.

Hence, only one beat per second will be heard.

SIMILAR QUESTIONS

Q1

In case of the mechanical longitudinal wave y = A sin (ωt – kx) in air (density ρ), what is the relation between displacement amplitude and pressure amplitude?

Q2

A man beats a drum at a certain distance from a mountain. He slowly increases the rate of being and finds that the echo is not heard distinctly when the drum beating is at the rate of 40 per minute. He moves by 80 m towards the mountain and finds that the echo is again not heard distinctly when the rate of beating of the drum is 1 per second. What is the original distance of the man from the mountain?

Q3

In an experiment, it was found that a tuning fork and a sono-meter emitting its fundamental note, gave 5 beats per second both when the length of the wire was 1 metre and 1.05 metre. The velocity of transverse waves in the sono-meter wire is:

Q4

A slab of mass m is released from a height h0 from the top of a spring S’ of force constant  K. The maximum compression x of the spring is given by the equation:

                                                                           

Q5

A bob of mass m is oscillating as a simple pendulum with maximum amplitude θm. What is the maximum tension in the string?

Q6

A certain amount of acoustic energy is emitted in a uniform hemispherical pattern from a point source. At a distance of 5 m form the source the intensity is 5 W/m2. At a distance of 15 m the intensity will be:

Q7

 A 10 W source of sound of frequency 1000 Hz sends out waves in air. The displacement amplitude at a distance of 10 m from source will be: (Given velocity of sound = 350 m/s and density of air = 1.29 kg/m3)

Q8

The air in a closed tube 34 cm long is vibrating with 2 nodes and 2 antinodes and the temperature is 51oC. What is the wavelength of waves produced in air outside the tube when the temperature of air is 16oC?

Q9

The fundamental frequency of a longitudinal vibrating of a rod clamped at its centre is 1500 Hz. If the mass of the rod is 96 g the increase in its total length produced by a stretching force of 10 kg weight will be:

Q10

The speed of sound waves in dry air at NTP is 332 m/sec. Assuming air to be composed of oxygen and nitrogen in the ratio 1:4 and the densities of oxygen and nitrogen at NTP to be in the ratio 8:7, the velocity of sound in oxygen will be equal to: