Question

A magnet oscillating in a horizontal plane has a time period of 2 second at a place where the angle of dip is 30^o and 3 seconds at another place where the angle of dip is 60^o. The ratio of resultant magnetic fields at the two places is

• A. $\frac { 4 \sqrt { 3 } } { 7 }$
• B. $\frac { 4 } { 9 \sqrt { 3 } }$
• C. $\frac { 9 } { 4 \sqrt { 3 } }$
• D. $\frac { 9 } { \sqrt { 3 } }$

Answer 1

Answer: (C)

$\frac { 9 } { 4 \sqrt { 3 } }$

Answer 2

$\Rightarrow \frac { T _ { 1 } } { T _ { 2 } } = \sqrt { \frac { B _ { 2 } \cos \phi _ { 2 } } { B _ { 1 } \cos \phi _ { 1 } } }$

$\Rightarrow \frac { B _ { 1 } } { B _ { 2 } } = \frac { 9 } { 4 \sqrt { 3 } }$