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5.Magnetism and Matter
hard
Two bar magnets of the same mass, length and breadth but magnetic moments $M$ and $2\,M$ respectively, when placed in same position, time period is $3 \,sec$. What will be the time period when they are placed in different position
A
$\sqrt 3 \,\sec $
B
$3\sqrt 3\, \sec $
C
$3\,\sec $
D
$6\,\sec $
Solution
(b)In sum position $T \propto \frac{1}{{\sqrt {{M_1} + {M_2}} }}$and in difference position $T \propto \frac{1}{{\sqrt {{M_1} – {M_2}} }}$
$ \Rightarrow \frac{{{3^2}}}{{{T^2}}} = \frac{{2M – M}}{{2M + M}} \Rightarrow {T^2} = 9 \times 3\,{\sec ^2}$
$\therefore \;T = 3\sqrt 3\, \sec $
Standard 12
Physics
