Question

Two magnets of same size and mass make respectively 10 and 15 oscillations per minute at certain place. The ratio of their magnetic moments is

• A. 4 : 9
• B. 9 : 4
• C. 2 : 3
• D. 3 : 2

Answer 1

Answer: (A)

4 : 9

Answer 2

$T = 2 \pi \sqrt { \frac { 1 } { M B _ { H } } } \Rightarrow \frac { T _ { 1 } } { T _ { 2 } } = \sqrt { \frac { M _ { 2 } } { M _ { 1 } } }$

$\Rightarrow \frac { M _ { 1 } } { M _ { 2 } } = \frac { T _ { 2 } ^ { 2 } } { T _ { 1 } ^ { 2 } } = \frac { ( 60 / 15 ) ^ { 2 } } { ( 60 / 10 ) ^ { 2 } } = \frac { 4 } { 9 }$