question_answer

A tuning fork of frequency 100 when sounded together with another tuning fork of unknown frequency produces 2 beats per second. On loading the tuning fork whose frequency is not known and sounded together with a tuning fork of frequency 100 produces one beat, then the frequency of the other tuning fork is                                       [NCERT 1977]

A)            102

B)            98

C)            99  

D)            101

Correct Answer: A

Solution :

           Suppose nA = known frequency = 100 Hz, nB =? x = 2 = Beat frequency, which is decreasing after loading (i.e. x¯) Unknown tuning fork is loaded so nB¯ Hence nA ? nB ¯ = x¯        ... (i)             Wrong              nB ¯ ? nA = x¯       ... (ii)             Correct Þ nB = nA + x = 100 + 2 = 102 Hz.