A current carrying coil is placed with its axis perpendicular to $N-S$ direction. Let horizontal component of earth's magnetic field be $H_0$ and magnetic field inside the loop be $H$. If a magnet is suspended inside the loop, it makes angle $\theta $ with $H$. Then $\theta =$
${\tan ^{ - 1}}\,\left( {\frac{{{H_0}}}{H}} \right)$
${\tan ^{ - 1}}\,\left( {\frac{H}{{{H_0}}}} \right)$
$\cos e{c^{ - 1}}\,\left( {\frac{H}{{{H_0}}}} \right)$
${\cot ^{ - 1}}\,\left( {\frac{{{H_0}}}{H}} \right)$
The values of the apparent angles of dip in two planes at right angles to each other are $45^{\circ}$ and $30^{\circ}$ respectively. The true value of angle of dip at the place is ............
A compass needle will show which one of the following directions at the earth's magnetic pole
At a certain location in Africa, a compass points $12^{\circ}$ west of the geographic north. The north tip of the magnetic needle of a dip circle placed in the plane of magnetic meridian points $60^{\circ}$ above the horizontal. The horizontal component of the earth's field is measured to be $0.16 \;G$. Specify the direction and magnitude of the earth's field at the location.
Angle of dip is $90^o$ at
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 $B_1/B_2$ is best given by