Question

Two bar magnets of the same mass, length and breadth but magnetic moments M and 2M 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. $\sqrt { 3 } \mathrm { sec }$
• B.
• C. 3 sec
• D. 6 sec

Answer 1

Answer: (B)

Answer 2

In sum position $T \propto \frac { 1 } { \sqrt { M _ { 1 } + M _ { 2 } } }$and in difference position $T \propto \frac { 1 } { \sqrt { M _ { 1 } - M _ { 2 } } }$

$\Rightarrow \frac { 3 ^ { 2 } } { T ^ { 2 } } = \frac { 2 M - M } { 2 M + M } \Rightarrow T ^ { 2 } = 9 \times 3 \mathrm { sec } ^ { 2 }$

$\therefore T = 3 \sqrt { 3 } \mathrm { sec }$