Question 85: Magnetism and Matter

Question

A magnetic compass needle oscillates 30 times per minute at a place where the dip is 45o, and 40 times per
minute where the dip is 30o. If B1 and B2 are respectively the total magnetic field due to the earth at the two
places, then the ratio $${{{B_1}} \over {{B_2}}}$$ is best given by :

Accepted Answer

$${f_1} = {1 \over {2\pi }}\sqrt {{{\mu {B_1}\cos {{45}^o}} \over I}} $$
$${f_2} = {1 \over {2\pi }}\sqrt {{{\mu {B_2}\cos {{30}^o}} \over I}} $$
$${{{f_1}} \over {{f_2}}} = {{{B_1}\cos {{45}^o}} \over {{B_1}\cos {{30}^o}}}$$
$$ 	herefore $$ $${{{B_1}} \over {{B_2}}} = 0.7$$

Answer

1.8

Answer

2.2

Answer

0.7

Answer

3.6

Magnetism and Matter

A magnetic compass needle oscillates 30 times per minute at a place where the dip is 45o, and 40 times per minute where the dip is 30o. If B1 and B2 are respectively the total magnetic field due to the earth at the two places, then the ratio ${{{B_1}} \over {{B_2}}}$ is best given by :

Choose the correct answer: