question_answer

On sounding tuning fork A with another tuning fork B of frequency 384 Hz, 6 beats are produced per second. After loading the prongs of A with some wax and then sounding it again with B, 4 beats are produced per second. What is the frequency of the tuning fork A [MP PMT 2000]

A)            388 Hz                                     

B)            380 Hz

C)            378 Hz                                     

D)            390 Hz

Correct Answer: D

Solution :

                   nA = ?, nB = 384 Hz x = 6 bps, which is decreasing (from 6 to 4) i.e. x¯ Tuning fork A is loaded so  nA¯ Hence nA¯ ? nB = x¯            Correct            nB ? nA¯ = x¯            Wrong Þ nA = nB + x = 384 + 6 = 390 Hz.