Question 88: Magnetism and Matter

Question

A magnetic compass needle oscillates 30 times per minute at a place where the dip is 45
o
, and 40 times per
minute where the dip is 30
o
. If B
1
and B
2
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 45 o , and 40 times per minute where the dip is 30 o . If B 1 and B 2 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: