Question

Two magnets held together in earth's magnetic field with same polarity together make $12\, vib - \min ^{-1}$ and when opposite poles together make $4\, vib-\min ^{-1}$. The ratio of magnetic moments is

• A. 9 : 1
• B. 1 : 3
• C. 1 : 9
• D. 5 : 4

Answer 1

Answer: (D)

As, $\frac{M_{1}}{M_{2}}=\frac{T_{2}^{2}+T_{1}^{2}}{T_{2}^{2}-T_{1}^{2}}$
$=\frac{n_{2}^{2}+n_{1}^{2}}{n_{1}^{2}-n_{2}^{2}}=\frac{4^{2}+12^{2}}{12^{2}-4^{2}}$
$=\frac{160}{128}=5: 4$