5.Magnetism and Matter
hard

Two bar magnets having same geometry with magnetic moments $M$ and $2 M$, are firstly placed in such a way that their similar poles are same side then its time period of oscillation is $T_{1}$. Now the polarity of one of the magnet is reversed then time period of oscillation is $T_{2},$ then

A

$T_{1} < T_{2}$

B

$T_{1}=T_{2}$

C

$T_{1}>T_{2}$

D

$T_{2}=\infty$

(AIPMT-2002)

Solution

When similar poles are on same side time period of oscillation $T _{1}$ is given by $T _{2}=2 \pi \sqrt{\frac{ I _{1}+ I _{2}}{\left( m _{1}+ m _{2}\right) B _{ H }}}$

$m _{1}=2 m , m _{2}= m$

$T _{2}=2 \pi \sqrt{\frac{ I _{1}+ I _{2}}{(3 m ) B _{ H }}}$

When the polarity of magnet is reversed, time period of oscillation $T _{2}$ is given by

$T _{2}=2 \pi \sqrt{\frac{ I _{1}+ I _{2}}{\left( m _{1}- m _{2}\right) B _{ H }}}$

$T _{2}=2 \pi \sqrt{\frac{ I _{1}+ I _{2}}{ m B _{ H }}}$

From above Equations

$T _{1}< T _{2}$

Standard 12
Physics

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