Question

A magnetometer is in $\tan A$ position. A magnet produces a deflection of ${30}^o$ in the needle. The no. of such similar magnets must be tied together such that like poles are touching each other to increase the deflection to ${60}^o$ is :

• A. $4$
• B. $3$
• C. $5$
• D. $2$

Answer 1

The correct option is B $3$

The relation between angle deflected and the magnetic moment is given by
$\frac{M_1}{M_2}=\frac{\tan {\theta }_1}{\tan {\theta }_2}$
$\frac{M_1}{M_2}=\frac{\tan 30}{\tan 60}=\frac{\left(\frac{1}{\sqrt{3}}\right)}{\sqrt{3}}=\frac{1}{3}$
$M_2=3M_1$
Therefore , 3 similar such magnets are needed.