When two tunning forks A and B are sounded together , 4 beats per second are heard . The frequency of the fork B is 384 Hz . When one of the prongs of the fork A is filled and sounded with B , the beat frequency increases , then the frequency of the fork A is

Options

A. 388 Hz
B. 389 Hz
C. 380 Hz
D. 379 Hz

Answer

A

Explanation

Let the frequency of the fork A be `v_(A)`
As it produces 4 beats per second with the fork B of frequency `(v_(B)=) = 384 ` Hz ,
` :. " " v_(A) = v_(B) pm 4 = ( 384 pm 4 ) Hz`
` = 388 Hz or 380 Hz`

When one of the prongs of A filed , its frquency increases .
If `v_(A) = 380 Hz` further increase in`v_(A) ` will result in decrease in the beat frequency when sounded with B .
If `v_(A) = 388 ` Hz , increase in `v_(A)` will result in increase in the beat frequency when sounded with B .
Thus , the frequency of the fork A is 388 Hz .