Question

A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per minute at a place where dip angle is 30^o and 15 oscillations per minute at a place where dip angle is 60^o. The ratio of total earth's magnetic field at the two places is

• A. $3 \sqrt { 3 } : 8$
• B. $16 : 9 \sqrt { 3 }$
• C. 4 : 9
• D. $2 \sqrt { 3 } : 9$

Answer 1

Answer: (B)

$16 : 9 \sqrt { 3 }$

Answer 2

By using $T = 2 \pi \sqrt { \frac { I } { M B _ { H } } } = 2 \pi \sqrt { \frac { I } { M B \cos \phi } }$

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