Waves Test - 13

 Answer :- a

Solution :- Let original freq. of sitar string A be na and original freq. of sitar string B be nb

As number of beats/ sec. = 6

∴ nb = na ± 6=430±6=436 or 424Hz

When tension in A is reduced, its frequency reduces 

(∵n∝√T) 

As number of beats /sec decreases to 4 therefore, frequency of 

B=430−6=424Hz

Frequency of fork one is 346 Hz.
When the other fork is waxed, the beat is increased.
So, the frequency of other fork is less than the frequency of fork one.
So, 
beat = frequency of fork one − frequency of second fork
4=346− Frequency of second fork
Frequency of second fork =350 Hz

A tuning fork is made of an alloy of steel, nickel and chromium, called elinvar, i.e. the material for which the elasticity does not change.

Radar uses electromagnetic energy pulses. The radio-frequency (rf) energy is transmitted to and reflected from the reflecting object. A small portion of the reflected energy returns to the radar set. This returned energy is called an ECHO. Radar sets use the echo to determine the direction and distance of the reflecting object.
It does not work on phenomena of beats.

For the formation of distinct beats, frequencies of two sources of sound should be nearly equal, i.e., difference in frequencies of two sources must be small, say less than 10. The impression of sound heard by ow ears persists on our mind for 1 /10th of a second. If another sound is heard before (1 /10) second passes, the impressions of the two sounds mix up and our mind cannot distinguish between the two. In order to hear distinct beats, time interval between two successive beats must be greater than 1 /10 second. Therefore, frequency of beats must be less than 1 0,i.e., number of beats/sec, which is equal to difference in frequencies of two sources must be less than 10. Hence the two sources should be of nearly equal frequencies. 

According to the Principle of Superposition, if the particle of a medium is given an order (i.e. of oscillating sinusoidally) and then another order (similar or different), the particle simply adds the two orders vectorially (i.e. by vector method), and then oscillates by the amplitude of the resultant vector.
So if the particle of a medium is given two similar orders (i.e., both the sine waves having the same amplitude, say A) then the particle will oscillate with an amplitude, 2A, i.e., the amplitude will be doubled.

As we know time interval will have dimensions of time so check in option for dimension of time.
Dimensions of v is "per second" or [T^-1]

Number extra waves received from each side:

n = +- u/λ

where

u= speed of the observer

λ = Wavelength of sound

Number of beats:The number of beats is given by the difference between number of extra waves received on either sides.

The beat frequency is always equal to the difference in frequency of the two notes that interfere to produce the beats. So if two sound waves with frequencies of 258 Hz and 256 Hz are played simultaneously, a beat frequency of 2 Hz will be detected.