Two tuning forks A and B produce 10 beats per second when sounded together. On slightly loading fork A with a little wax, it was observed that 15 beats are heard per second. If the frequency of fork B is 480 Hz. what is the frequency of fork A (in Hz) before it was loaded?

Let v1 be the frequency of A and v2 that of fork B.There are two possibilities (a) v1 > v2 and (b) v1 < v2. (a) v1>v2:v2=480Hz,vb=10HzNow, vb=v1−v2∴ v1=v2+vb=480+10=490HzOn loading fork A its frequency decreases. In other words, v1 decreases.∴v1−v2=vb should also decrease. But vb increase to 15 beats/s. Hence v1 is not greater than v2. (b)  v1