Question

Two magnets placed one above the other oscillate with a period of 6 sec. If one of them is reversed, the time period becomes 2 sec. The ratio of their magnetic moment is nearest to

• A. 7/3
• B. 5/4
• C. 7/4
• D. 7/5

Answer 1

The correct option is B 5/4

$Solution:$

Let the magnetic moment of the two magnets be $M_1$ and $M_2$Then,

$6=2\pi \sqrt{\frac{1}{(M_1-M_2)B}}$ and $2=2\pi \sqrt{\frac{1}{(M_1+M_2)B}}$

$\Rightarrow \frac{M_1+M_2}{M_1-M_2}={\left(\frac{6}{2}\right)}^2=9\therefore \frac{M_1}{M_2}=\frac{5}{4}$

$So,the$ $correct$ $option:B$