Two bar magnets having same geometry with magnetic moments M and 2M, are firstly placed in such a way that their similar poles are same side then its time period of oscillation is T₁. Now the polarity of one of the magnet is reversed then time period of oscillation is T₂, then

When similar poles are on same side time period of oscillation T₁ is given by 

$\begin{array}{l}{\mathrm{T}}_2=2\pi \sqrt{\frac{{\mathrm{I}}_1+{\mathrm{I}}_2}{\left({\mathrm{m}}_1+{\mathrm{m}}_2\right){\mathrm{B}}_{\mathrm{H}}}}\\ {\mathrm{m}}_1=2\mathrm{m},{\mathrm{m}}_2=\mathrm{m}\\ {\mathrm{T}}_2=2\pi \sqrt{\frac{{\mathrm{I}}_1+{\mathrm{I}}_2}{\left(3\mathrm{m}\right){\mathrm{B}}_{\mathrm{H}}}}\dots .\text{ (i) }\end{array}$

When the polarity of magnet is reversed, time period of oscillation T₂ is given by

$\begin{array}{l}{\mathrm{T}}_2=2\pi \sqrt{\frac{{\mathrm{I}}_1+{\mathrm{I}}_2}{\left({\mathrm{m}}_1-{\mathrm{m}}_2\right){\mathrm{B}}_{\mathrm{H}}}}\\ {\mathrm{T}}_2=2\pi \sqrt{\frac{{\mathrm{I}}_1+{\mathrm{I}}_2}{{\mathrm{mB}}_{\mathrm{H}}}}\dots \left(ii\right)\end{array}$

On comparing Eqs. (i) and (ii), we get T₁ < T₂