question_answer

When a tuning fork A of unknown frequency is sounded with another tuning fork B of frequency 256 Hz, then 3 beats per second are observed. After that A is loaded with wax and sounded, the again 3 beats per second are observed. The frequency of the tuning fork A is [MP PMT 1994]

A)            250 Hz                                     

B)            253 Hz

C)            259 Hz                                     

D)            262 Hz

Correct Answer: C

Solution :

                   It is given that nA = Unknown frequency = ? nB = Known frequency = 256 Hz x = 3 bps, which remains same after loading Unknown tuning fork A is loaded so nA¯ Hence nA¯ ? nB  = x        ... (i)               Correct              nB  ? nA¯ = x        ... (ii)              Wrong Þ nA = nB + x = 256 + 3 = 259 Hz.