A bar magnet A of magnetic moment MA is found to oscillate at a frequency twice that of  an identical magnet B of magnetic moment MB when placed in a vibrating magnetometer. We may say that

Frequency of bar magnet A is twice the frequency of bar magnet B. Thus if T be the time period of oscillation of B, then time period of 4 will be T/2. HenceT2=2πIMABH and T=2πIMBBHThe two expressions show that MA = 4MB.